Im looking at buying a 99 4runner with 118000 miles on it. I have never owned a toyota before but am rather knowledgeable about mechanics of cars. My problem is the car is supercharged which is awesome but I was wondering if anyone else out there that has a super on there runner could answer me some questions. Will the supercharger effect the durability of the motor (will it last as long)? should I expect any problems out of the supercharger with that high of mileage? is it costly to have work done to the supercharger?
PLEASE HELP!!!!!

Don't have a SC, but in general a vehicle with a super or turbo charger could be problematic.
1) It could have been driven hard by an owner taking advantage of the HP.
2) If it wasn't serviced right the engine and/or SC could suffer.

An example, Toyota had a turbo charged version of the 22RE (22RTE) 4 cyl in the 86-88 time frame.
If it wasn't cooled down properly after being driven (ie, let it idle for a few minutes before shutdown) turbo life was shortened. Few lasted more than 100K mi or so.

Also, most SC/TC engines require hi octane gas, people cut corners there due to gas prices.

And rebuilding or replacing a SC or TC is not cheap.

Just a little FYI.

I am assuming you have the 3.4L engine and the factory blower. I don't own a turbo truck, so a Google search would be a good idea.
I do know the 3.4L V6 is one overbuilt engine. Box stock it makes 200HP, but can easily take the 400HP the blower should bump it up too. With a proper balancing, minimal engine work, and a lot of boost, people are seeing 600HP out of the engine. With the exception of any trouble spots (search Google), you should be good.