Did you install SP1 for XP? I think it's required for drives larger than 137Gb... At least that's what the box says on the WD 250Gb I got this AM at Fry's...

XP Service Pack 1 (SP1) adds support for 48-bit Logical Block Addressing (LBA) for ATAPI drives, which lets the OS access hard disks larger than 137GB (the current limit). For this change to work, you must also have a 48-bit LBA-compatible BIOS

To enable 48-bit support, do this:

- Start regedit.exe
- Navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\atapi\Parameters registry subkey.
- Edit, New, DWORD Value.
- Enter a name of EnableBigLba.
- Double-click the new value, set it to 1.
- Reboot.

I hope this helps, but Iìm not usre this actually is your problem.

Also, are you sure your ram modules are ok?