In Windows Vista it is now possible to resize partitions without any data loss in the new Disk Management console.

Resizing Partitions with Windows Vista:

1. Click on the Start Button and right click on Computer and select Manage.
2. Expand the Storage section and select Disk Management.
3. Then just right click on any partition and select either Expand or Shrink to change the size of the partition.

This will allow you to safely resize your partitions without any data loss.