Who'd Play Who
Chi-Chi- Julie Louise Dreyfuss (Seinfeld)
Gohan- Ewan McGregor (Episode I and Trainspotting)
Piccolo- Michael Dorn (Star Trek: the next generation)
I chose Elaine from Seinfeld because she is as overbearing and uptight as Chi-Chi is.  She also looks right.
There is no particularly good reason I chose Ewan McGregor, but I couldn't think of anyone else.  If he can go from playing Mark Renton to Obi-Wan Kenobi, he can play Gohan, too.
Michael Dorn has the perfect voice for Piccolo, and because of his Star Trek experience, he's used to wearing alien makeup.
Tien- Henry Rollins (Black Flag, Rollins Band)
Rollins would be a good Tien because he would make him look like less of a Nancy than in the anime and I want to see him with another eye.  Oh yeah, he has the muscles to be Tien, too.
Yamcha- Keanu Reeves (Speed, Matrix, ect.)
I chose Keanu to play Yamcha because they are both these wussy, pretty-boys who think they're tough.  Keanu looks a bit like Yamcha, too.
Master Roshi- Patrick Stewart (Star Trek: TNG)
If you ever saw the SNL episode where Stewart hosted, you'd understand this.  Captain Picard plays a hilarious dirty old man, plus he was the best Star Trek captain ever...yeah, you heard me, better than Kirk.
Vegeta- Nicky Katt (SubUrbi@, Boiler Room, Dazed and Confused)eget
Most of you I'm sure have no idea who this guy is, but he is the ONLY choice for Vegeta.  This guy has both Vegeta's looks and his attitude.  If you haven't seen one of his movies, go look for yourself, you won't be disappointed.
Bulma- Lori Petty (Tank Girl, A League of Our Own)
Lori Petty is fantastic, and you'd have no problem getting her to dye her hair blue.