I have used VirtualPC 5 to run Win98, Win2K, Linux/x86, AROS, Darwin/x86, OPENSTEP, and some other stuff.
VirtualPC is a very accurate emulator and is easier to use than a typical PC since you only have to deal with one configuration and set of drivers. If you use VPC I suggest using Win2K since it works better with 32bit clean software.
Whether it's fast or slow depends on what you want to use it for. If you want to run 3D games, forget it. However for my uses it's fast enough. For $100 is also pretty cheap.
