Help with problem

Hi guys,

I'm new here, since I just got involved in this after downloading PS 7.0 a few days ago.
I have a question about using the lasso tools to select parts of a car. If I make a mistake of some sort can I alter the selection without having to reselect everything all over again. I hope that made sense, and any help would be appreciated.
Secondly, below is my first attempt (I know its no good) and could someone advise me on how to smooth out the side skirt so it all looks as one piece and not so choppy.

http://img78.photobucket.com/albums/v291/dingo22/Aston-Martin-DB9-008_copy.jpg

Thanks

Just press shift down when u select if u wanna add things to the selection or alt if you wanna remove. to smooth lines u can do it with blur tool or (which i think is better) smudge tool that u find at the same menu :)