Perhaps you can try the Analyzer 2000 at  http://www.brownbear.de/
I downloaded it and seems nice (has a lot of added features besides the
scope). Have not put it to work yet.

The problem is that all this scopes that use the sound card is the aprox
20Khz limitation.
Does anyone know about any HW that can be built at home to get any of this
PC scopes to work above this range? This should not be a very difficult
thing (not much beside a fast A/D) but I have not the skill to design it.
Regards,

Esteban.