Network Problems

I currently have a DSL connection in my house. I use a Belkin Wireless-G Router and a Speedstream Modem. Since about lsat week, my connection will randomly drop, or lag really badly, but then moments later it will be fine. Also, sometimes it becomes so bad, that i must reset both the router and the modem. What could be causing this? It not just one computer either, all the computers on my network are experiencing this drop.