First of all, in case you are not familiar with what Virtual PC is, it is basically a software which emulates a PC and its associated hardware. For more details check out the wikipedia entry. It obviously has its business uses, but that does not mean that one cannot have fun with it.
It can be useful for running different operating systems on the same machine without making any changes to the host machine configurations. I have been reading up on different linux distributions over the last few days, and was looking for a way to try out some, especially now that many of the distros have live CDs. So, I gave it (Microsoft Virtual PC) a try yesterday. It’s quite simple to use and you can customize the configuration of the virtual PC to a fair extent, including the RAM, hard disks and other drives. Once I had set up a couple of virtual PCs, I needed some OSes to run on them. This is where the linux live distros (Puppy Linux and Damn Small Linux being the smaller ones) and FreeDOS came in handy.
Once you start up your virtual PC, you need to have a bootable device (virtual hard disk/floppy/CD) in place so that you can actually use it. In case of the linux live distros, they can be run directly off the CD, and you do not really need to install them on the virtual hard disk. In case of FreeDOS, you can mount the CD image and install it on the virtual hard disk. So, setting up a virtual PC is pretty much like setting up an actual PC, only much faster. As for network/internet access from the virtual PC, it is possible to configure a network adapter for it, but I haven’t tried it out.
So, what do you do with it once you’ve set up a virtual PC? Well, anything you like. Use it like a real PC, try out different stuff (including playing games). This way you can try out a new OS (granted it is available as a CD image), without actually reconfiguring or messing up your existing system.