I decided to bite the bullet and try the dd-wrt upgrade. Figured I had nothing to lose. If it worked I saved myself the expense of a USB wifi device, plus perhaps some frustration (my experience with those is that they aren't particularly stable). If I bricked the router I figured no big loss - I didn't have a use for it anyway. The upgrade was actually fairly easy. The dd-wrt instructions are a bit intimidating at first, but if you spend an hour doing your homework and downloading the right files for your router it isn't bad at all. Now I have a very stable wireless connection to the main router and everybody is happy!
Success! If I bricked the router I figured no big loss - I didn't have a use for it anyway. The upgrade was actually fairly easy.
Great that it worked for you. I have been very impressed with the versatility of the dd-wrt firmware. I have flashed several brands of routers with may versions of dd-wrt and never have lost a router. Just follow the instructions!