Another update!

QTParted seems to do what GParted cannot: It can resize fat32 partitions!

I'm trying it out on my 160GB USB HDD right now; I'm shrinking the fat32 partition to 133 GB and adding a 16 GB ext3 partition.

EDIT:
QTParted is great. It seems much more polished than GParted; it doesn't need a list of devices (it detects them all) and it has better info.

Here's a screenshot post-successful-repartition!



EDIT2: It doesn't seem to handle the SD cards very well, however. It shows every partition as a separate device. I wonder if that's an artifact of the chroot mounting process? Hmm.