If you have the drive completely dedicated to Linux partitions, XP won't install. You need some free (as in unallocated) space for it to find - or a pre-setup NTFS (primary) partition.
You've been changing so much, it's hard to know what's what. If it was me, I'd erase the (terabyte) drive, and unplug the 750 Gig (just to safe). Then install XP - minimises the chances of things winding up in the wrong place.