Shrinking system partition

I have a dual-boot configuration with XP on my C partition, also the
system partition, and Vista on my V partition. I also have several
partitions in between including G immediately following C. What I'm
trying to do is insert a new partition between C and G, shring either
C or G or both. Although I have 5.37 GB free on C, Computer Management
shows only 23 MB available shrink space, even though I moved XP's page
file to a different partition and deleted its hibernate file. Is there
anything I'm missing or is it the fact that it's my system partition?
Drive G reports 1.7 GB free, all of it shrinkable.

Thanks in advance,
Boris Zakharin