I have done this, but it was a royal pain in the butt and cost me an extra $20 (US). Assuming you are using a couple of WRT54G/GS routers (Linksys), here is the guide that helped me do it.
You will need to either download the Freeman or Talisman firmware and install it on your router (voiding the warranty if you still have one). DO NOT use the firmware that this guide recommends. I suggest using the Talisman firmware because the company that makes it will give you tech support.
DO NOT use this firmware if you aren't using a WRT54G/GS router! It will permanently break your hardware!
Feel free to post any further questions, and I'll *try* to answer them. If you aren't using the above routers, please post which ones you are using.