My friend owns a 97 blazer and he said that he is losing power when he accelerate, kind of a rough idel, and hard starts. Also when you put your hand behind his exaust you can feel the heat kind putter like the engine is missing.

Sounds like he needs a tune up.

What does everybody else think?

How many miles? Was a tune up ever done before?

Plugs, wires, cap/rotor, filters (fuel and air).

120,000 I don't think it's had one.

Pretty much the same as anything else: Start with a complete tune up,
plugs
wires
dist. cap
rotor
pcv
change oil/filter
air filter
Than check / clean egr, clean MAF, etc.
Beyond that, coil, IAT, etc.
If he hasn't done a tune with that many miles, he also may want to flush rad., change all diff/tran/transfer case fluids, grease the front end. One great saturday project! get him to buy the lunch and some liquid refreshment, and give him a hand. Than he'd owe you one.