You should be able to attach a hard drive (virtual) to the VM. Unless you chose the "allocate all of the disk space now" (non-default) when you created the VM, you should have free space. Or if you shutdown the other 08 VM, you can back it up directly into the 08 VM. The former option is better. Attach a VHD of desired size, back up to it, then detach it and attach into your new VM.