Partioning problems in Vista x64

[someone1029]

Hi all, I want to dual boot xp x64 with my recently installed copy of vista x64, but vista won't let me make a partion bigger than 799962MB and I wish to make a 200GB partion (on a 298GB (actual size) drive, leaving 98GB for vista).

How can I make a partion this size and, why won't vista let me shrink the drive more?

[someone1029]

I really need this sorted out. Surely someone could help me.

I had a thought. If I backup my entire boot drive with the vista backup utility. Install xp, repartioning/formatting the drive in the process. Then install vista in the partion I leave empty and use that to recover my previous install of vista.

Would this work (my main concern is being able to recover my previous install) and is there any easier way?