Listen, I actually want a music mixer like GarageBand. Yeah, i know EVERYONE here will force me to audacity, but I don't have any instruments I can record on my computer, and can't afford to get any. Also, I need it to be frickin' better than mario paint. I mean. no offence, but you can actually get a bit of 8-bit music composed, without almost any experience.
In short terms:

I want a free audio sequencer with audio samplers like GarageBand but on nifty ol' Linux, Mandriva to be exact. I tried to install Freecycle and try it, but my Mandriva decided it was gonna be an evil biotch and make a dependency so one needs the other and vice-versa. At the same freekin' time.

I'm not sure if any are a perfect fit for you, but I'd check out Rosegarden, Ardour, and LMMS.

Linux Journal has also been doing a series of audio articles that might prove informative. The most recent is about loop based composition.