(at least I think it's alt+f2) both of these kill your x session, what commands do these button combinations initiate? I got music to play when I boot (mpc play) and stop when x starts (added mpc stop to startx file in bin) but what exactly happens when I press ctrl+alt+Backspace or alt+f2?

When you're in an X session, like Gnome, XFCE, Fluxbox or KDE; the "alt + f2" it simply brings up a 'run' dialog box. The "ctrl + alt + backspace" is called 'zap' and it will end your X-session and applictions, zapping them. This can be turned off by the sys admin if required. If you were using run-level 3 (default Slackware boot admin configured /etc/inittab controls this) it will bring you back to the prompt that has your user name, you're still logged in. That is the place you typed 'startx --nolisten tcp' at. If you were using run-level 4 then it would zap X, and restart it bringing you back to GDM, SLIM, XDM, or KDM or whichever graphical log-in user interface you use. Or if you have auto-login turned on for a particular user account, it would bring you back into that user's X-session.