I don't know what this Rip software that Sac speaks of is supposed to do; I've never heard of anyone else using such.
As far as printers go, you'll want to get an Epson if you're printing transfers yourself. This is because some Epson printers (not all) use pigmented inks instead of dye-based inks -- that means the prints won't bleed the first time the shirt is washed. The transfer will still probably look okay if printed from an HP (or whatever), but it adds another notch of professionalism if the shirts don't bleed like that. If you go this route, make sure you get a printer that does indeed use pigmented inks, such as the OEM Epson Durabrite inks. I think you can get a new one, not on sale, for around $100; I'm not sure of the model names offhand since I don't deal with prnter that much.