I would try having the motherboard run the longer self check before messing with the memory. The memory's probably ok, anyway, but I'm just checking.

As far as I know, you can't get a virus just from mapping the drive, but once you run a program, it could give you a virus.

I was actually getting ready to blame the network card, because mine was giving me problems until I switched it over to a different PCI slot. I don't remember what the problems were, tho. But it looks like your network card's been working fine for a long time with no problems, so that's probably not it.