Use the sveasoft firmware. I dont know if it works with the older 802.11b, but I know it works with the Linksys 801.11g (54mbps) routers.
I havent tried it, but I know this works. You install the new firmware onto the router (go into your internet browser and type
http://192.168.1.1 , you can find a way to install the firmware <a .bin file> onto the router).
With the new firmware, again type
http://192.168.1.1 into the browser, and you will be given a whole bunch of new choices, including those that allow you to
increase the router's default transmittal power of 18mw to variable settings up to 84mw!! This can drasticly increase your wireless range.
Also, it supports a "client" mode that can repeat signals. Say that you have a cantenna, and you have gained permission from your neighbor to borrow their internet. Plug up the cantenna, turn on client mode, aim, and your router now repeats your neighbor's signal!
You can download it here:
http://wrt54g.thermoman.de/FreemanBasic ... wrt54g.zip