A 3TB hard drive,while cheap,will not work in the following machines.
Here is why,so if older computer,forget about it.New hard drive discs of 3 tb are GPT,only latest windows support it,older windows uses MBR system and they cant use anything BUT MBR.
However you can use 3tb as an external backup hard drive,but you wont be able to boot windows from it.
So 2 TB is max for a bootable win XP system. =========================================================== If you have a new large hard drive (> 2TB) in your system Purchasing a large size hard disc (with capacity more than 2 TB), a user may get into difficulties with allocating free space beyond 2 TB because of the following reasons:
MBR limitation: an MBR partition layout can only address only up to 2^32 x 512 bytes (up to 2 TB of all available disc space);
GPT limitation: a GPT partition layout allows addressing large discs, but some operating systems do not support working with GPT discs, such as Windows XP;
Booting from GPT discs: only Windows Vista SP1 (x64) and Windows 7 (x64) support booting from GPT discs on UEFI systems;
UEFI: UEFI is a new BIOS technology and is not supported on all computers;
Windows XP (x32) is unable to detect discs larger than 2 TB properly;
USB controllers: some USB controllers may not allow recognition of the correct size of the large disc.