Hmm. I'd suggest finding a download site. Hey! Isn't that convienant? This is one!
Alright, now select the car you want and click "Download". Some downloads require VCMM((Vice City Mod Manager)). I prefer those because I'm lazy. Download that, which also happens to be on this site. Then open the download in VCMM and click "Install", I think. Well, whatever it is, it's pretty self-explanitory.