I've personally only used a Valuline 1000w switchable ballast (so its MH or HPS), and it was a great product, however it seems the 600w is HPS only.

I would definately get a upgraded air cooled reflector, it will help you suck most of the heat right out of your cabinet, a large inline duct fan might be pretty good if your trying to save money, but if your friend is giving you a decent size squirrel cage fan, that should work even better.

Theres a lot of options, you just have to figure out what would be best for your situation. I would just make sure you get more then enough ventillation on your first purchase though so you dont waste all that money and have heat issues still.