when you flip your STOCK front rims you will gain an inch of width on both sides. but if you have a 2003 or newer you will have to install shorter valve stems to flip them. with the 88-02 models you simply take your wheel off and flip it so the stems are in.
no you cant do it for the back end. but if you want to widen the rear you can get some spacers for fairly cheap, or get a stock banshee axle and widen it out that way