DSL connection dropout

I set up a wireless G router to use with a DSL modem. The router was set for PPoE and connected successfuly to SBC, the ISP. The wired connection to the router works fine. The wireless connection drops out anywhere from 1 minute to 15 minutes. Reconnecting is always successful only to dropout again soon. I tried the Linksys WRT54G and the D-Link DI-624 and I tried several channels. Anybody has any suggestions? I’m out of ideas. Thanks