Sam: Don't know much about your age, ability, conditioning, buddies, finances, etc., so it's hard to get too specific. At my age (60) I'd have to go guided, but perhaps it could be different for you.

There are several good books on the subject ("Float Hunting Alaska's Rivers" is one title, I believe), plus you could probably Google all sorts of info.

Whatever route you take, Good Luck! (And don't wait until you're 60 to give it a whirl!)