To the OP,
First off, Roddick serve info is everywhere on the net. Simply google 'roddick serve' or 'roddick abbreviated serve' or something (or search here in 'tennis tips'.) Alternatively, Tricky posted some excellant stuff on this as well - search it out.
Secondly, I did exactly what you're attempting. After a lot of work (and I mean A LOT), my clunky, malfunctioning pinpoint serve improved into a far smoother, simpler and consistant serve. Nowdays, it has evolved in a few areas too so it isn't a carbon copy of A-Rod's (not that I ever had anything of his pace - I can only wish!) Anyway. I think it's great to emulate this style - (although abbreviated or semi-abbreviated motions apply to so many pro's now, such as Henin, Monfils, Gasquet, Nadal, etc - it really isn't unique to Roddick) - because it forces you to remove the variables; that which is surplus, and concentrate on the fundamentals.
Some important things as I remember them regarding A-Rod serve:
1) DEEP DEEP DEEP LEG BEND!... Roddick has an unreal leg bend in terms of depth (and it's about the only thing I've ever heard him comment upon himself in relation to his serve)...
2) DOWN & UP, JACK-HAMMER MOTION!...Roddick doesn't so much spring forwards and up in the conventional sense as jerk down very hard and up... very abrupt... think Hammer...
3) STUDY HIS FEET!... no-one in tennis serves with their feet placed so close together!... He also does a weird kind of synchronized stepping up and down on the balls of each foot routine (I could never quite work it out)... but simply serving with your feet so close together aides the above ^ tip on 'the hammer' and really helps you feel like Roddick (you'll also find your butt sticks out! - really!)
4) LOWER YOUR TOSS!... His toss is a bit lower than is conventional... (It's also unfailingly consistant, which helps!)
5) EXHALE SHARPLY ON CONTACT!... If you study closely and study enough you'll see he sometimes blows out as he strikes the ball...(it's true!)...
6) EXTREME RACQUET DROP!... Synonimous with the huge leg bend is the way he drops the racquet behind him so very low (and at a unbelievable speed)...
Anyhow. That's what I can recall for now. Hope it helps...