No partitioning software will cause data loss. PartitionMagic and Built-in Partitioner in Vista and 7 all work fine. If you're using XP, you need PQMagic. For Vista and 7, the built-in is ok but can't move data around so it works best after a clean install or with a good defragger like PerfectDisk that can move everything around including pagefiles and system restore images.