yeah, you can have as many colours as you like, but jvaska said, are you printing spots? is it just a home thing or a proper printing job you're working on??? if it's a personal home thing, what printer are you using? if it's an epson photo for example it's best if you send the job in rgb as it uses it's own rgb-cmyk convertion, anything else, it needs to be cmyk, as these are the only inks the printer has (yes i know some are more than 4 colour now, but let the printer handle that).
if it's a job that's being sent to a press, each additional colour costs, a lot.
in quark just go to the colours palette, from there you can create anything, spots, pantones, mixes, duotones etc etc.