But back to your question, with my P166 box I can mix about 14-16 mono tracks in realtime. But I'd say that no machine is too slow or too fast for ecasound. You have a link to the free music site at your music page. Yep, this a hot topic right now. Like with software, I think it's important to make a distinction between 'free' and 'gratis'.
Free music is more about freedom to create, copy and distribute.
For instance, I'm about to release my 2nd demo-cd, Bulky Material. Just like with my first demo-cd, all the tracks are freely available on my web site. But this doesn't stop me from selling the cd version. Similarly, distribution of mp3s is not free. Someone has to pay for the web space and the net bandwidth.