Connection drops

Another problem im having is after my PC is on for a while, sometimes the Internet connection goes out. Sometimes it doesnt at all, sometimes 5 minutes later I have nothing. But if AIM, or BitTorrent is on, that stays connected, I just lose Web, and email, and nothing can connect after that. I have to restart to get everything back. I have an SMC Router (but only my PC is affected by this), I am on a cable modem, built in LAN in my mobo (Asus P4S800D)....I dont know where else to turn...I almost bought another network card, but someone told me that may not work at all.....any thoughts?

I am also behind Zonealarm, but also the little icon in that system tray with the 2 computers...the lights are always flashing...and device manager says Network card is working properly....any guidance is appreciated....thanks in advance!