All you really need to know is that the special sauce lies in embedding Linux in your router and then converting this into a powerful, highly configurable $600 router. Here I am going to walk you through upgrading your router firmware to the powerful open source DD-WRT firmware.
What you'll need:
One of the supported routers. I used a Linksys WRT54GL Wireless router that I picked up from Newegg, and the instructions that follow detail the upgrade process specifically for that router and its close siblings. If you're upgrading one of the other supported routers, you might want to look into instructions specific to your router. These instructions may generally work for other supported routers, but I'm not making any promises.
The generic DD-WRT v23 SP1 mini firmware version
The generic DD-WRT v23 SP1 standard firmware version
You'll be upgrading the firmware twice, first using the mini firmware, then using the standard.
Boost your wireless signal
The first thing I did after I finished the firmware upgrade was give my wireless signal a much needed boost ("needed" in the sense any signal boosting that can be done needs to be done, right?). Doing so is trivial.
Go to the Wireless tab, then to Advanced Settings. Find the entry labeled Xmit Power, which is set by default at a paltry 28mW, and can be set up to 251mW. To be honest, I don't know much about the science of the whole process, but I do know that 251 is WAY bigger than 28. However, you probably don't want to pump it up to 251mW right away.