Ran into a few problems today, for one client who uses a VPN that doesn't work at all well with Vista, I have an XP development virtual PC. I needed to install visual studio sp1 (yet again) on it but my boot drive only had 4Gb of free space - the temporary installer needs more than that.
After finding the excellent VHD Resizer I was able to resize by virtual disk by an additional 10Gb, however it doesn't extend the disk into this space and diskpart won't let you issue an extend command on the boot disk.
The solution? Boot off another VHD with the resized disk as a second drive, then extend under this environment before shutting down and setting it back to the newly extended drive.
Full answer here...