I have a fixed size virtual hard drive that is running out of space. What's a good way to go about increasing the size?
This VHD is created from Microsoft Virtual PC and/or Microsoft Virtual Server.
There's a free utility you can download called VHD Resizer that should simplify this task.
There is also a step-by-step walkthrough of the entire process that might be of help.
You could use the /extend switch of Microsoft's VHD Tool.