Your bios has to support large drives and you need to partition the drive as GPT instead of MBR. Windows 7 can boot from > 2TB drives as long as your motherboard supports EUFI and the drive is partitioned as GPT.
It doesn't matter if it's just storage, it must still be partitioned as GPT in order to see the full 3TB. Since XP doesn't support GPT, it will only see the hidden MBR block within the GPT partition thus restricting you to 2TB or less partitions.
If your motherboard doesn't support large drives than GPT makes no difference. I found the specs online and it uses a phoenix bios V6. This should support large drives. I think XP is holding it back.
Hawkeye is correct. Windows XP 32-bit will not be able to access beyond 2TB on a GUID Partition Table (GPT) formatted drive. You will need to reformat the drive using Windows XP and select the "Format using GPT" option in order to access the 2TB (of the the 3TB availalbe). Your other best option (and most recommended) is to just go out and buy Windows 7 Home Premium 64-bit. No one in their right mind would run XP anymore! Just saying