Modern routers can do all sorts of complex tricks, but sometimes you just want to use a a spare router for a simpler task, like extending your existing wireless coverage. That's where open source firmware DD-WRT comes in.
Over at Mobile Mojo, Anthony Caruana runs through how he used the well-regarded DD-WRT to make a Linksys WRT310-N into a basic access point. Replacing the existing firmware with DD-WRT made that a one-click affair. Hit the link for the details. If you want to soup up your router instead, check out our previous guide to building a super-router with Tomato
Router Modding with DD-WRT and the Linksys WRT310N [Mobile Mojo]