|I assume this is something you've just noticed or maybe you just installed the drive?|
Is the bios showing it as 32 or as 80? If the bios says 80 but the OS is showing 32 it could be because you have a FAT32 partition. XP will only create a FAT32 partition of 32 gig or less. If it's an NTFS partition then either is was originally created as just 32 gig or maybe a FAT32 partition was converted to NTFS. You should be able to check all that in Disk Management.
If the bios is showing it as 32 gig (and you're talking about the 2.8 ghz computer described in your specs) then you probably have it jumpered with a 32 gig clip. That's designed to be used with older bios' that couldn't properly see large drives. The bios would see it as 32 gig and then you'd install a drive overlay in order to use the drives entire capacity. Your 2.8 ghz machine is new enough that is doesn't need that.
Real men don't use AntiVirus; they just reformat