i know i'm not much help.. cos theres a website, but im not sure of name.. and they put any picture you want on a t-shirt.. you just mail them it!
if not you can DIY by using image maker and a t-shirt... dead easy , get a colour photocopy (must be a photocopy, printer inks don't work) and u put the paste on teh back of the paper when the image is face down on the t-shirt (text must be reveersed) and tehn when the image maker has dried (overnight i think) then u sponge off the papaer with a damp sponge and voila! (instructions r given sdo i dunno why i wrote that!)