Everyone has giving you some nice tips and yes you DO NEED photoshop or a similar program, you can't get by with paint. The modeling is only 85% of it and with proper textures you can make or break a model. It is going to be tough at first, your going to start and not have a clue what anything is or does. Tutorials are your friend (and there are a lot of them now days) until you get the hang of things. Start small with importing different wheels, lightbars and get use to moveing and placing those items. Don't try and scratch model right away, you have to crawl before you can walk.
Tom is right, piracy is a big no no here but PM him, it seems like he's going to give you a private speech on piracy