I know some of you will like to crucify me, saying this is unethical, etc., but whatever. You're stealing TV, so 'borrowing internet' should be the least of your worries.
And you're all going to be doing this anyway, especially people with laptops with no internet sub, that steals their neighbors wireless anyway. So here goes:

c/p-

First off, you need to install DD-WRT on your linksys router- use wiki or google to find out how to do this. Install/flash all firmware needed. Then, make sure DD-WRT is set to all FACTORY DEFAULTS (Administration tab/Factory default).


Intro-


In the real world, you might own only one router which can run DD-WRT. Thanks to the new V24 beta firmware, a single DD-WRT router can be set up as a wireless repeater. Unlike a WDS, your DD-WRT router can now receive and redistribute a wireless signal from a generic AP.

Typically, you would use wireless repeater mode to rebroadcast a signal too weak for your wireless clients to pick up reliably – assuming that your DD-WRT router can pick up the host AP, of course. In a test case, I successfully repeated a host AP with a signal strength of only 9% as seen by the DD-WRT router – so low that the host AP wasn’t detected at all by a laptop's integrated wireless.

Wireless repeater mode also groups your local clients into their own subnet – a potential feature (for privacy) or a potential hassle (for LAN routing), depending on your needs.

To set up a wireless repeater yourself, you’ll first need to upgrade your DD-WRT compatible router to the latest V24 beta. If you are currently running a DD-WRT setup, take a moment to back up its settings before flashing to V24 (Administration/Backup), in case you later decide to revert to your original configuration.


Router Setup


Take note of any wireless security currently enabled on your host router. If you are using WEP, note your passphrase and key length (64-bit, 128-bit, etc.). If using WPA or WPA2, note your passphrase. Later, you’ll need to use these to set up your repeater. Note that because DD-WRT V24 is still a beta, your mileage may vary when it comes to repeating a secured host router. Users of earlier betas reported a number of problems, but these seem to be smoothed out with the latest releases (the V24 1/15/07 release, as I write this).

Also make note of the SSID of the host AP you want to repeat. Alternatively, you can scan for available APs from within the router’s administration interface as well.

You will need to access the administration interface of the DD-WRT router you’re setting up as the repeater. Connect a wired PC to the DD-WRT router. Be sure to disable any wireless adapter on your PC for now, and plug the Ethernet cable into one of the LAN (not WAN) ports on your DD-WRT router.


Step By Step

Assuming your DD-WRT is set to factory defaults, its IP address is 192.168.1.1. If your client PC is configured to receive an IP automatically, it should be assigned an address by the router.

Step 1. Open a browser on your PC and connect to the DD-WRT router – its default address is http://192.168.1.1. The default login is root and password is admin. Of course, you should change these. If you don’t, you’ll have bad dreams involving Sally Struthers and bathing.

Step 2. Click Setup/Basic Setup. You can leave Connection Type at its default, “Automatic Configuration – DHCP.” You can leave the router and host name fields at default if you like, or customize them as we did.

The most important setting here is the Local IP Address. This must be a different subnet than that which the host AP is on. Our host AP is on 192.168.1.1, which was also the default for this DD-WRT router. Thus, we’ve changed the DD-WRT router to 10.0.0.1.

You can leave the remaining settings alone – the DHCP enabled, etc. – and click Save Settings at the bottom of the page. Your router will reboot.

Because it will restart with a new IP address, you will need to repair the client connection at your PC to join the new subnet. (Otherwise, you won’t be able to access the administration page any more.)

In Windows XP, navigate to Control Panel/Network Connections, right-click on the Local Area Network connection, and choose “Repair” from the pop-up menu.

Once reconnected to the router, you should open your browser to its new address – in this example, http://10.0.0.1.

Step 3. Click Security/Firewall and click to Disable the SPI Firewall. If you want any special firewall settings, you should configure these on the host router.

Step 4. Click Wireless/Basic Settings. For Wireless Mode change the selection from its default “AP” to “Repeater”.

Unless your host router is set to G-only mode, leave Wireless Network Mode set to “Mixed”. If your host router is set to G-only, likewise choose “G-Only” here.

Set the Wireless Network Name (SSID) to the SSID of your host router. If you don’t know it and for some reason can’t figure it out, we’ll show you how to scan for it a little later.

Leave the remaining settings at their defaults. Some claim that setting Sensitivity Range (ACK Timing) to 0 improves performance, which you might experiment with once the repeater setup is tested and working.

Important: Now click Save Settings. The page will then refresh.

At this point, you have essentially set up the DD-WRT router in wireless client mode. Your PC that is wired to the router should be able to access the Internet, assuming that the host router can.

The next step is to enable the DD-WRT router to behave as a wireless AP in addition to being a wireless client. That’s why they call it a repeater, mmmkay?

To perform this trick, you will create a Virtual Interface. This will behave as a software AP, broadcasting its own SSID and bridging external wireless clients to the router, which is itself a wireless client to the host router in this configuration.

Click the Add button and the page will refresh again, with new fields for configuring the Virtual Interface.

Fill in Wireless Network Name (SSID) with the name you want for the repeated wireless network. For best results, this should be different from the SSID for the host router. You will see this SSID available when your wireless clients scan for access points.

Leave the remaining fields at their default values as seen here, and be sure to click Save Settings.

Step 5. Click Wireless/Wireless Security. In repeater mode, you need to consider two dimensions of security:

First, is security enabled on the host router that you’re repeating? If yes, you’ll need to configure security on the DD-WRT router’s “physical interface” to match.

Second, do you want security between your repeater and local wireless clients? If so, you’ll need to configure the kind of security you want on the DD-WRT router’s “virtual interface” and, of course, on each individual wireless client that associates with the repeater.