I used my older WRT54G v 2.0 and installed the open source firmware from http://www.dd-wrt.com (this site has firmware for LOTS of routers though, not just the one I happen to have. see http://dd-wrt.com/wiki/index.php/Supported_Devices ).
Once the firmware is installed (see http://dd-wrt.com/wiki/index.php/Installation ) there is a tutorial on using the open source firmware to use the router as a wireless bridge (see http://dd-wrt.com/wiki/index.php/Wireless_Bridge ).
I would always get stuck spinning my tires when following the tutorial above though, but feel free to give it a try - or just try what I did (after flashing the firmware of course):
I'll try to give generic directions:
Primary Router (hooked up directly to Cable Modem):
**Note that there should be very few - if any - changes to your primary router settings**
~Has a standard Security/IP setup, we'll say WPA Personal Security Mode, TKIP Encryption, and an IP of 192.168.1.1.
~Enable the DHCP Server and give it a range of however many IP addresses you wish. I'll use 10 for this example, starting with 192.168.1.2 and ending with 192.168.10.11.
~SSID Broadcast must be "ON".
My Secondary Router Setup - I'll call this the Bridge from now on:
~Make the IP address of the Bridge the first IP address in your DHCP Server range of the Router (192.168.1.2 in this example).
----If you plan on using the Bridge as another wireless access point, then simply enable the DHCP Server on this also, and give it a (different!) range of IP addresses.
~Under the "Status > Wireless": click "Site Survey". A list of all visible wireless networks will pop up in a new window. Click "Join" (you may have to scroll to the right...) on your network.
----This will automatically change pretty much all settings to what they should be - the only thing I had to do (if I remember correctly) manually was change "Wireless Mode" from "Client" to "Client Bridge" under "Wireless > Basic Settings".
~Just to be safe, make sure your SSID, Wireless Network Mode, Security Mode, Shared Key, etc match your Primary Routers Settings
MAC address info: Any devices (PSP, Laptop, etc.) that you will be connecting to the web through the Bridge may also need their MAC Addresses input into the Bridge's MAC Address Filter.
Last, the tutorial says to check the "Assign WAN Port To Switch" box under "Setup > Basic Setup". I do not have this checked and am fully functional.
Hope this helps. Any questions can probably be answered somewhere on the dd-wrt.com site. Or post them here and I'll be glad to help.