Seriously, you can get the most awesome bikes off ebay. Usually they're even better priced when you get an XL like you would need. I would look for perhaps a Gary Fisher Wahoo, or something from Giant. As for your girlfriend they have good junior sized bikes at wal mart. Just kidding, really, im just being ********. Giant also sells great bikes for women, the rainier W looks like a good deal, but im no expert on womens mtb's either.
I wouldnt perticularly recommend a mongoose if you plan to use it for trail, they're not built as well as many other bikes are going to be alot heavier and have troublesome componentry.
Oh, and also check out the trek website, they make basically everything good.
Last edited by elf 232; 03-02-08 at 09:51 PM.