How do you increase the size of a Boot Camp partition?
Use iPartition. It makes a boot DVD you can use to repartition your drive. It supports repartitioning Boot Camp partitions. I've used it twice with no issues for this purpose.
A free solution is CampTune. I've never used it so YMMV.
This guy seems to have it all figured out:
Citing his blog:
To increase the size of your Windows partition use the following steps.
I like his approach, because it just makes sense - is straightforward and seems like you could not do it any simpler. Also backing up your partition on an external hard drive is always good, in case something goes wrong.
If you follow his directions you will have two backups - a windows backup made by Windows and also a clone made by Winclone.
Besides WinClone he uses BootCamp assistant to create partitions and resize them, so you get as close to the original as possible.