Gear problems and possible replacement rear wheel advice

kingstonkev Posts: 2
edited October 2010 in MTB beginners
Hello All,

First post on the forum, I'm hoping you guys can help me out with what is probably something pretty basic.
My brother kindly gave me his old 96' KHS Montana COMP MTB, it hasn't been ridden for a few years : ... otostream/

The main problem I have is with the gears, either the chain will slip off completely and get stuck between the frame and the low cog of the 7 speed cassette or this will happen : ... otostream/
Here is another view : ... otostream/
I've tried making a couple of adjustments but to be honest I'm probably doing more harm than good as I don't really know what I'm doing. What could be causing the chain to slip off like this and how can I stop it from happening ? Also, when the chain does stay on it won't go through the gears properly, it either gets stuck or changes at random.

The rear wheel seems to have a very slight buckle, it isn't knocking against the brake pads but it doesn't seem to be "true", it's a 26" Weinmann Bontrager, should it be replaced ? What would you suggest I replace it with ? Could this be the cause of the gear problems ? I'm aiming to commute to work on this bike and do some off road stuff when I can.
Thanks for your help,