[URGENT] USB based spectrum analyzer (oscilloscope) or HP dynamic signal analyzer?

I want to get a spectrum analyzer to learn and view charactarictics of various audio shaping circuits (so I'm staying in the DC - 20KHz region). My options are getting a 150$ - 200$ USB based scope that comes with a spectrum analysis software. There are various manufacturers here but the spec. is pretty much the same. The other options is to get an HP dynamic signal analyzer which is as-far-as-I-can-tell a spectrum analyzer for low freq. I am pretty sure the HP can get the job done - it's a non-nonsense piece of gear, however it takes up space, more expensive and in terms of outputting the data for logs and charts on a computer it lacks behind. My question is, can I get away with using a USB based solution? Just looking for a couple of opinions here...

How about Visual Analyser? It's free software that simulates various instruments including oscilloscope and spectrum analyser. Input is through the soundcard of your PC.

WOW that looks outstanding. What about that kit from the magazine? Do you have it?

No, I haven't tried any of it - just remembered seeing it on the web.