When I go to partition the disk, only half of it is there. Google is showing me little. Makes me guess that it's a ide/motherboard type problem. I'm not sure where to begin reading.
If it's 256GB, chances are it's due to a combination of windows itself and the motherboard. You'll need to use a utility (usually free from the hard drive maker - check their website) to partition and format it, then you'll be ok.
I know in xp before service pack 1, it will only recognize at most 136 gig drive (Its some where around 136, I can't remember the exact number.) My guess is Win2k has a similar limitation...