I would throw on a tora solo air or a reba. Both are good forks for the price and tunable. You can run 100mm travel without too much issue but there isn't a point to put more unless you're doing riding other than xc, in which case I would consider getting a different bike.
As far as installation, check out park tool's mechanics corner.
http://www.parktool.com/repair/readhowto.asp?id=111