Paragon software has made available a pre-release version of Camp Tune, a new utility for resizing your Boot Camp partition without destroying data. While the Leopard version of Disk Utility is now able to perform partition resizing, it is not able to resize a Boot Camp partition without erasing it (although you could back it up and restore it if needed). Camp Tune runs as a bootable Linux-based CD which allows you to boot your Mac and reallocate disk space between your Boot Camp and HFS+ partition.
Camp Tune for Mac is presently in pre-release and is being offered as a free download (registration required). The download is a disk image that must be burned to a CD or DVD. Needless to say, you should have a backup for both partitions before using any software of this sort.