What the hell is WRONG with this computer!

My friend as a Computer:

Pentium II 500mhz
128MB RAM
ASUS P2B MB
ULTRA TNT 2 (I believe it's a creative)
Hard-drive 1) IDE (possibly Maxtor)
Hard-drive 2) SCSI (A/V drive)

For some reason, when he is hooked up to a LAN (at our lan partys), ANY file he trys to download off any other computer ends up being corrupt. It doesn't matter what. Game demos, game patches, whatever. It does raise hell as sometimes only one person has a patch for a particular game and he can't get the friggin thing to work because it always ends up corrupting itself somehow. Sometimes the error message says that a transfer error possibly has occured.

He's tried Win98, Win98 SE, Win ME, and Windows 2000. He's tried different network cables and different network cards. And I believe his main hard-drive is brand new, and it still does it. (It did it on the old one too) It still does the same thing. Corrupt, corrupt, corrupt.

What gives? Has his motherboard kicked the bucket?