So then whats virtual PC? It lets you run windows programs.
Virtual PC runs on PowerPC machines and emulates an Intel processor and PC BIOS, so that you can run Windows as an application on your Mac. Although it comes with a copy of XP, it's much faster if you only run Windows 95 or 98 on it. This is fine if you'll only be using it occasionally.
A couple of points though. Firstly, it's not quick. Even on my 1.9GHz iMac G5 I only get equivalent performance to a Pentium 400MHz or so. Secondly, it's useless for games since it will only emulate an old S3 Virge graphics chipset.
However, if you only want to run MS Project, Internet Explorer to check website compatibility or some other piece of software that isn't available for Mac then it's okay.
Just as a matter of interest, what is the software you want to run? There may be a Mac equivalent program that runs natively on OS X.