first off, what are some good scales for making metal/heavy rock/whatever? i took lessons for a couple of weeks and the guy only taught me harmonic minor... everything i try to make with it sounds really dark and classical. I really only know that and pentatonic minor so any good sounding scales that i can memorize and screw around with would be great.

second off, what's the difference between a scale and a mode? i've been trying to pick up what theory i can lately, but this still confuses me.
Run a seach for good scales for metal. I think I've seen quite a few threads on that.

A mode is a scale.
I play metal, so I can probably help you out. When I write my songs, I use a lot of diminshed scales, minor scales, and actually some pentatonic blues scales(they can turn out metal). I do like using the chromatic scale every once in a while, because that can turn out great results(Master of Puppets).