I bought my new g4 and I did not realize that there is no serial port. How should I go about using my serial motu xt? Is there a good serial to usb converter? Will that work? Am I stuck buying a new interface? Any help is much appreciated.

If you are on OS 9 the best solution is a stealth serial port or a Griffin Gport.
They both replace your built-in modem with a serial port.
I am not sure whether they are compatible with the latest g4 models (they are however compatible with quicksilver G4 models).

http://geethree.com/p_stealth.html

http://www.griffintechnology.com/products/...port/index.html

Please note however there is not currently (and probably never) any way to get you MIDI interface to work in OS X!