If you play games a lot, Evil Player is for you. It runs on Vista flawlessly and can run just about any music file with it. It has beautiful global hotkeys that are easy to learn and use. I mean... it's features are just really nice, its easy to use and takes up very little speed.

http://www.hakeem.gigahost.dk/

Using the Bento theme, the miniplayer mode just moves the player into the bottom right, which only obscures the entire system tray and a chunk of the toolbar. I'll check it out on the default theme.

Evil player lacks .m4a support.

You could always use this skin for Winamp.