well there are the: rc,alpha,beta,unstable releases.What are the differenses with all these from a stable release ???
I'm mostly interested for RC releases coz i wanna get rc releases for alsa and some other stuff.

Stable normally means that that version of an app is considered quite robust and is suitable for use in a production environment. Unstable versions can sometimes be very stable in practice but aren't considered mature enough to be used in critical situations.

Alpha is the very first initial development releases of an app and are usually pretty crude. Beta is the next step along, the app is more developed but not fully polished and completed and is still undergoing testing, hence the expression "beta testing." rc = release candidate, the final testing releases to iron out the last bugs before a stable release.

tnx man...another question: can u go from RC---->stable by just aplying a patch or that depends from the developer ??

I'm asking that mostly to learn if this procedure is adapted with the kernel upgrade system.(via patches)