Disk management has limited partition resizing, you can only shrink a partition until it hits a system file and you cannot shrink the front of a partition or "slide" anything.
There are several free partitioning tools, partition wizard works and looks like partition magic did.
gparted is another free tool I hear a lot about.
Make sure you backup everything to be safe and for best results do all partition work outside of windows from the bootable CD.
Dave