You can get as big of a hard drive as you need. The only trouble you'll have is that the legacy formatting scheme, MBR, only supports up to 2TB. You'll have to reformat it as GPT (Windows 7 can do this). The issue with going GPT however, is OS's (or their versions) older than Windows Vista won't recognize it (I could be wrong).
You also can't boot on partitions formatted in GPT unless your BIOS supports a work around or are using UEFI.
How about we split it into 2 partition each @2TB or split into another 3 or 4 partition? I think we can still use the older tipe of partition scheme