Lattitude 700m-WLAN connected but internet works 10 minutes only

Hi everyone - really been getting frustrated by this...I've been trying to figure out a confusing problem on a laptop and I'm hoping someone can help...I'm working with a dell lattitude 700m, running windows XP home and using an intel 2200bg wireless card. The laptop will browse the web perfectly upon bootup for about 10 minutes - after that, the connection to the router remains intact, but every web page I try to visit times out. Strangely, I'm able to successfully ping these sites without trouble from the command prompt. At first I thought this was just the wireless, but the result is the same when physically connected to my router. Additionally, after I lose browsing abilities, I'm able to use FTP services, windows file sharing, AIM, limewire and any other program that requires the internet - I can even view https sites in the web browser - but when I go to any "normal" website I get time out messages. I tried updating the wireless card drivers, ensuring TCP/IP settings were clear, running a full spyware scan, ensuring there was no proxy info in my web browsers...I even used winsock fix and scanned for malicious LSPs. No luck! I still cant browse the web for more than 10 minutes. I have no security software running aside from windows defender (and with this disabled the result is the same). I used a ubuntu live CD to boot into linux to aid my troubleshooting - within linux internet access works fine for as long as I need it to, so I've eliminated the possibility of this being a hardware issue. I love ubuntu, but this laptop isnt for me - it's for someone who needs windows. If you have ANY ideas I'd be very eager to hear...thanks!