I used to like my Toyota Supra which was painted like the Toyota Castrol Supra. I can't upload a pic though as I sold my xbox, I do miss Forza though, I wish they'd bring it out on the PC like they did with Halo.
The R8 is an DLC, or free if you bought the Greatest Hits edition (how I got it). You will need an HDD if you wanted to install the disc that came with the Greatest Hits.
The Forza 2 greatest hits was a really nice offer. Since it was only $30, and it came with the game, and all the DLC released (including the 350Z that was pre-order only). I guess that's one of the perks of getting it late.
That's what the livery editor is for. You can do any kind of graphics you want, you just have to actually create them shape by shape. If you browse Forza forums, you'd be blown away by some of the stuff people create.