open up the hood and look down at your belt. You see the bottom most pulley?
take that pulley off (4 bolts)
then get a harmonic balancer removal tool (like 10 bux at harbor freight)
remove the balancer. Make sure you back the bolt out of it first. It is a 15/16" bolt with a washer on it. if you can't break it loose, put the car in gear and put the e-brake up. use the instructions on the removal tool to remove the balancer (rather easy)
get some rtv and put it on the keyway (metal tab sticking out from crank..can't miss it)
get the new balancer and slide it on (this can be a PITA...try taking a propane torch and heating inside the balancer a bit so it expands and goes on the crank easier.
get it on far enough to where you can get the bolt and washer to go back in about 5 threads or so. From there you can draw it on SLOWLY by tightening the bolt. Torque it down to 108 ft/lb (I could be wrong on this spec). If you feel it binding up..DON'T FORCE IT ON!!!!
It really isn't that hard.
before you do this though...I'd check basic things. A bad plug wire can cause a bad vibration. do a simple tune up first (cap and rotor, plug wires, etc.) Also, I'd go ahead and pull codes and do a cylinder balance test (the instruction book will tell you how to do this)