Resizing a Virtual Disk
Once you have created a virtual disk (and possibly installed an operating system on it), its maximum size is fixed, even if it is a dynamically expanding disk. So if the virtual disk has a maximum size of 10 GB, it will never grow beyond that size, and Virtual PC itself is not capable of resizing. There is, however, a way around it, which we will go through step by step.
Source: kb.dutchalps.com