Vista - Vista locks itself...?

I booted back into XP MCE 2005 to try to give Vista more space on its
partition (it's only at 20 GB right now), and so I opened PartitionMagic.
When I got there, two things happened:
1) The partition, which I had named Vista (from within Vista itself), was
now named with several symbols.
2) The Vista partition - with about 9.5 GB free space when I'd left Vista -
was marked as completely full. So was the 160 GB drive I'd designated for
backup.
When I tried to redistribute the free space among my partitions, it wouldn't
let me select that one. I tried to copy the files away to resize it
afterwards, but that didn't work, either. It appears that Vista locks down
its drives and partitions when it's not in use, but that 20 GB is going
fast... any way I can get to them? I'll try to get PartitionMagic on my
Vista install if I need to...