The setup is main PC connected through WIRED router and a laptop with wireless connection. We have had constant cut offs for some TIME. We contacted our ISP who carried out many tests and said that the problem was not with them, to contact the manufacturers of the router. This we did and Linksys tried everything they could think of over 3 days, but still no luck. The laptop is connecting at great speeds, but the main PC is almost at a standstill. In desperation we formatted the PC but the problem REMAINS! so we have come to the conclusion it must be Lan card. Is this possible? or can anyone else think of a reason for this to happen.
We are using XP Pro, IE,have anti virus and spybot, adaware etc installed and used frequently please can someone help? Are you using onboard LAN? Whether onboard or an add-on card, I think I'd buy a PCI card as the next step in trying resolve this. Here's what newegg.com has:

http://www.newegg.com/Store/SubCategory.aspx?SubCategory=27&name=Network-Interface-Cards

I'm using one of these: D-Link DFE-530TX+ PCI Network Adapter - RETAIL. It's been working fine for me.Just thought I would let you know that in desperation I uninstalled Windows update
KB951748. after reading of the problems with Zone Alarm. I have NEVER had Z.A but thought I would try getting rid of this update. Hey Presto! everything started running correctly again. Weird or what?

Interesting....bug in the update or maybe was modified by something(maybe a virus)