Join Date: Oct 2007
Location: West Yorkshire, United Kingdom
If it fits, and everything works, you got a good deal, from the pictures, it doesn't look like it's been ridden off road a lot, if ever.
For rust, the frame is aluminum, so you shouldn't ever seen any on that, for the forks, once the corrosion has set in under the chrome, you can't really stop it, but you should get a long time out before it gets bad, from the pictures, there isn't any visible, so there can't be much.
From the look of the setup of the bike, the seatpost looks too low (with a 20" frame, guessing you are well over 6' / 183cm tall?) and would look at getting a shorter stem, that looks to be 110+, which is from the 90's, 70-90mm should give a much better ride.