No, no money deposit or credit card necessary.
None of the poker sites require those if all you want to do is play for play chips, or in a non-cash tournament of the sort Petra has in mind. The problem with the European site we tried was that the freeroll tournament tables were all in the "cash" section of the site, and because of an idiotic law passed with the encouragement of the holy roller Bush administration, U.S. players are not allowed to play in cash games, or games located in the cash section, of any foreign sites.
Yes you'll need to create an account on any site. All the sites ask for standard personal information (name address city state country), but if you're not playing for real money you can fill that in with anything you like, i.e. make all the info up if you prefer. The only accurate bit of information they require is a working email address so they can confirm your account once you register it.