I just replaced my lower intake manifold gaskets. There are a few really great sites that will give you all of the info that you need to access the heads. I did the job in 7 hours, first time ever doing it.
If you are planning on doing it yourself, I have several helpful links to share.
You have to follow torque specs and torquing patterns to THE LETTER when you re-install the manifold cover. You also have to be VERY careful when cleaning the heads as to not get any debris into the crank... cover it up, and use NON abrasive material to wipe or "buff" them clean.
I have to agree with Roy though, if you are not familiar with your engine you have to LEARN it all first. It also helps to tape and mark components as you go if you are not 100% certain. It is a great way to learn the engine, and will save you in excess of $400.