You don't need any special soundcard to use Riff Interactive guitar lessons. As long as you can hear what we're doing, you're fine. If you're talking about doing live private lessons with Riff Interactive technology and Microsoft NetMeeting, you only need a fast Internet connetction, a web cam with mic, and almost any soundcard.
The soundcard I use is the Audigy 2 by Creative.
It works and sounds good. I have a small Mackie line mixer between my synths, mics, and guitar pre-amp, and the stereo line in of the sound card. The out of the soundcard goes to a stereo reference amplifier to the studio monitors for hi-fi playback. No sense in having a nice sound card if you are using cheap power and speakers.