You probably don't want to do dye sublimation. In my opinion, there are too many limitations (have to use poly/cotton tees), and you won't be able to print on dark garments.
Your options for printing on dark garments are screen printing, opaque heat transfers, screen printed transfers, and vinyl cut transfer (I may be leaving one or two options out).
If you do a google images search for dye sublimation, you'll run across some images of t-shirts printed with this method. For screen printed t-shirts, just take a look in your local target or something (or your closet). Most t-shirts you see in stores are screen printed.
If you want to do heat transfers and are looking for a printer, check out the Heat Transfer section of this forum and do a search for printer

Or just look at some of the recent threads in that forum for printer and press suggestions.