Wireless connection "collapses"

[kaptainkikote]

I recently bought a Dell 500 m (centrino with built in wireless card)
I also installed a d link 900 AP+ behind my ISP CPE (a Zyxel Prestige 643 router).
Sometimes my wireless connection works great. Others the connection is establishes (eg I can cross-ping computers) but access to the internet from the laptop is very slow or just does not happen at all.
Any idea why this could be? running windows XP home.

Thanks!

 

[JP5]

what encryption are you using?