Whenever I do these touchups myself I'm pretty disappointed with my results, but maybe you'll do better than I do and/or be less particular about how they turn out.
Standard touchup: get some *good* touchup paint (I get mine from
PAINTSCRATCH ). I get *MUCH* better results when I use a small artist's brush (maybe size 00 or so) as opposed to a paper match or toothpick (let alone the brushes that come with touchup paints, don't even try using those). You apply a little color/base coat and then fill the scratch the rest of the way with clear. Then consider wetsanding to level it with the surrounding paint. Then polish to remove the sanding scratches. There are some threads that explain this in detail. Your damage sounds pretty significant though, no way I'd try this if your car has metallic paint, it just won't work out very well.
Better touchup: search for Brad B.'s thread about how he used an airbrush to do an incredibly great touchup on his silver Porsche. That is how to really do it right. Takes an airbrush (and air supply) and more skill than I believe *I* have, and I know my way around my Paasche brand airbrush

But plenty of people can do stuff that I can't do, maybe you're one of 'em.
Best touchup for those of us lacking Brad's skill: take it to a good paintshop and have a repair spotted in. I'm having this done right now on my MPV and I'll be having it done soon on my M3- both vehicles have damage similar to yours. No way I can do as good a job as those guys will do so I just pay the bill. Not sure how much it'll cost but it's not a lot...consider that it doesn't take hours on end to do such a job and shop rates vary from around $30/hr to $75/hr, plus a bit for materials. Honestly, IMO this is the no-brainer choice for most people, the challenge is in finding a decent shop to do the work.