XP without a Service Pack or XP SP1+?
Probably around 800Gigs. I can't be sure. I don't think though that it matters, it will support anything, internally or externall, it just won't be able to Format it or recognise it in the Disk Management.
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.