I work alot with Sharepoint, and have created myself various Virtual Machines for different configurations and some for presentations with a rollback to reset everything back.
One common error I also run into is assigning to little space on the virtual hard disk and thus running out of disk space. There is no real way to increase the hard disk space, although you can change the sizes of the partitions.
I found VHD Resizer, which resizes your VHD to any size you wish. But note you will have to increase/decrease the partition on the disk though.