program 2 plug in cart :view setup workon monitor

I just thought why can't a program be set up to take the same info that dealers us when they use an ocilliscope to straighten the angle (and get the little elipses crossed,) on the home computer.
With the standard XP and such, I would think a program could be a fast bit of fun for a geek. and to be able to plug the cart straight into an adapter to a port, and see the same info as the ocilliscope would be worth $29.95 anyday. (And I can't spell ocilly scope and too excited to look it up.)
Anyone know of such a program or device? (besides the real thing ocilliscope!)
I believe that there already are devices that have scope hardware to hook up to your computer so you can use your monitor. I don't know how much they cost, or where to get them. But, it seems like I have read or heard about this product some time ago. I figure they are pretty expensive because you still need the hardware to do the interface to the computer.