Katie:

I agree with Jim wholeheartedly and encourage you to put a lot of thought and research into this very important decision.

Whatever tripod/head combination you get, it should be sturdy enough to provide a stable platform for the heaviest camera/lens you plan on regularly attaching to it, but light enough so that you are actually inclined to take it with you when you go shooting.

(This advice from a guy who leaves his home far too often and frequently comes home with less than stellar shots as a result.)

Tucson Jim