No experience with any of the other sites (tripod, et cetera), but MSN couldnt be much simpler when it comes to posting images.
All they require is a Passport account (which is free) and you're off and running.
If you need a hand setting it up, let me know...Id be happy to set up the account and community for you and give you the username password; simply change the pw to something you can remember and voila.