Linksys WRT54G2 Router

My roommate and I both have Intel MacBooks running 10.4 and we have a Linksys WRT54G2 router. Our third roommate has a Dell running XP, and she has no issues with the wireless. However, both of the macs can connect but the speed is very slow most of the time. On average, I'm getting less than 1 mbps, but the connection is really spotty and it will range from .17 mbps to 13 mbps in less than 10 minutes. We've tried connecting straight to the modem via ethernet and I got between 15 and 20 mbps, so we know it's the router. We've tried playing around with the settings on the macs and the settings for the router, but nothing's helped. Any suggestions for what to try?