The beer can shouldn't be able to rise above the boiling point of the liquid inside until it is empty. Your chicken should be finished cooking long before that.
Obviously, the aluminum of the can itself isn't a safety issue anyway. If you are worried about the paint on the can, you can either buy the Poultry Pal that Sam linked to, or take some sandpaper to the beer can and scrape it all off (before opening the can of course).
For ease of removal later, you should be coating the can itself with fat/oil before inserting it into the chicken.
Cook slowly. Last time I made it, I aimed for about 275f to 300f. If you are doing it on the grill, use a pan to catch the drippings and prevent flare up.
I also basted occasionally to help create a more flavorful crust (not to prevent drying out, since the steam inside does that wonderfully).