why does my wireless network get disconnected so frenquently with a wireless router?

I once used a CompUSA wireless router to set up a wireless network for my two laptops at home. I could access internet immediately after setting it up. But after some while, the network got disconnected, I had to power down the router once, and then power it on so that the network could be recovered. Since then, the same problem could happen at least 3 times a day. Sometimes even if the wirless icon says "Singal Strength: Very Good", I still could not access the internet. Powering down once and then powering on the router seems the only and a very effective way to solve the problem, but it is so annoying.

I then bought a Netgear wireless router(Netgear Wireless Cable/DSL Router - 802.11b 2.4 GHz ),  I thought the new router would solve the problem. The first two days it worked well, but the third day the problem happend again, and I had to power down/on the router again to recover the internet access.

I was wondering how to make my wireless-network work without this powering down/on trouble.
My laptop is IBM T30 running windows xp professional. I have to use a "IBM Acesss Connection" wizard to configue the network. I set Wep for both the laptops and the router for security. I also did the things suggested in the following link and hoped to solve the problem permanently, but no luck yet.

Could anyone please help me get rid of this trouble?

Thanks a lot!