So far, Partition Magic has never messed up when I resized my Windows partition.
I highly suggest you back up your data, though. You may not be able to login anymore, this never happend to me when resizing the partition, but it happend when I restored an image on a partition that wasn't the same size as the original partition. Windows showed an error with something like "Hardware changed,...".
TheMajorMMX - Intel P200 MMX @ 225Mhz - V-Tech (PcPartner) Baby-AT mb w/ Intel Triton TX chipset - Nvidia Riva TNT2 M64 w/ 16MB - 256MB M-Tec SDRAM - Still running.....