First off all, for classical guitar DEMO CD you don't really need "Professional" software. As Joel suggested Audacity would be sufficient for laying stereo tracks and some editing. Just yesterday I've tested Focusrite Saffire using Audacity @ 24 bit/192 kHz sampling rate which is more than you need for demo project. Yep, I was surprised too. Audacity can go all the way up to 192 kHz and Cubase can't
As far as hardware is concerned, it all depends how much you want to spend. You can get Lexicon Alpha for around $130, Art Tube MP for $50 and M-Audio Pulsar for about $100 and you are good to go. Less than 300 bucks gives you decent quality if you are on the budget. Alpha even comes with Cubase LE which will let you add effects in addition to editing and of course sequencing. If you can spend more than sky is the limit.