Problems with wireless connection and browsers

[bolido2000]

I use a wireless router to access the Internet at home (D-link 624). The thing is that I usually leave the computer running downlowding stuff. When I came back to the computer a couple of hours later, Bittorrent and trillian are still connected to the internet and downloading data, but neithe IE or Firefox are able to access the internet. They keep timing out. I then have to restart WXP to regain access to the net with the browsers. What's causing this??