whs, you could use a VM to test out Win7 and you would not lose your changes each time. The Virtual Machine (VM) creates a virtual disk drive. Whether this is actually just stored in a file or uses an empty partition only matters to the software managing the VM. The Win7, or other, OS that is installed inside the VM sees the virtual disk drive as a disk drive. It has an MBR, partition tables, and all the rest. When you write data or make changes these are written to, for example, the C: drive as far as Win7 will know. When you shut down -- virtually shut down -- Win7, the VM session closes but all of the data saved to the virtual disk drive is still there. The next time you (virtually) boot Win7, it reads the partition table, finds the C: drive and reads it's data just as it was.
One drawback to running Win7 in a VM is that you won't experience the changes in speed. So, you won't know how fast Win7 will boot, shutdown, or run on your actual hardware only on the virtual hardware.