I know I should of just bought the SC but I didn't want to pay the premium price (gas). Is it possible to add that myself. I have worked on cars before at a garage so I do know how to do a some stuff. Is it worth it to add the SC or should I just do aftermarket things, filter, exhaust, plugs & wires, etc. Just lookin for ideas for more power.

If you bought it naturally aspirated, you should just keep it that way. It isn't worth the cost and downtime of your truck to do it. It is nice to have, but not worth adding as an aftermarket thing. It would probably be cheaper to trade your X in on a supercharged X.

Give this thread a look:
http://www.xterraownersclub.com/cgi-local/ultimatebb.cgi?ubb=get_topic;f=70;t=000053#000006

I installed a SC (from a kit) in my car about 10 years ago. And I'm still happy with it.

dave and xtoy - but would not bother with the x