Not sure if this will be of any help, but I bought a 3 TB Toshiba Canvio Desk DWC130 (3.5", USB 3.0 & 2.0, external power supply). The box lists Windows Vista as the oldest supported version of Windows, but it works perfectly fine when connected to my WinXP Pro (SP3, 32bit) system via USB 2.0.

Windows XP tells be that the drive has a capacity of 3,000,590,379,440 bytes (currently 2,008,704,225,280 bytes free). I didn't have to download new drivers either (that PC hasn't been connected to the internet for at least three years when I bought that drive). I didn't have to reformat it or anything (at least as far as I can remember - the drive still has the backup software on it that it originally came with).