Anyone know a good network diagnostic or PC component diagnostic app?

I have an aging PC running windows XP held together with little more than happy thoughts, but I have no money to upgrade it at this time. I have in it a wireless network card, a Linksys WMP54G4.1, and an onboard Intel NIC on an Asus P4P800-VM mobo that my landlord’s router starts to ignore after a couple of months. I’ve tried reinstalling the cards several times, and occasionally they connect for a few seconds. I know it’s a software problem because they work fine under any Linux distro, and when I reinstall Windows, which is the way I fixed them last time. I can’t use Linux without it crashing and dying after a couple of weeks, so that option’s out. I put a packet sniffer on both of the connections and they broadcast their DHCP and other requests fine, but get no response. Also, occasionally the others in this house have the same problem, but only for a few seconds, usually fixed by just disabling their connections and re-enabling them; a solution which does nothing for me. I can’t reset the router because the people that have connectivity don’t want to risk losing it again. Everyone’s on a wired network that utilizes those netgear converters that use the house’s power grid as a network; however, though the house is wired wrong and is aging, this provides no problems for the other users.

Does anybody know what in the Hel is going on?