For all practical purposes, there is no such thing as a PC scope with any kind of decent capabilities at all unless you limit yourself to audio work. You may see 100 MHz bandwidth, but with that you'll also see a maximum of maybe 100 MHz sample rate. The advice to get a good, used analog scope is good. There are a lot of good Tektronix, Hewlett-Packard, etc. high-end used scopes for under $200. Even ones under $100 will run circles around a PC scope. It's the difference between driving a Corvette and a virtual PC Corvette -- it may look and feel great and be cheap, but it won't get you anywhere.