If you want just to play, pc based scope is OK, but this is far from the real thing. Soundcard is limited by (too low) sampling rate, noise, input range, and other bad things...
Scope that use PC only for display results (also FFT, and some other things) with measuring done on scope side (A/D, uC...) is comlete another story, the real thing.
I found few diy projects on web (try to search), but there is no simple things. You need fast A/D converter, uC connected to memory chip (64k is more than enought), and some connection to PC.