I don't think there is much difference in there purpose!msn messenger is latest version i think,if you have a hotmail account you can set up messenger to use the same username and password .it is used to chat with friends and family or who ever .if you know someone who uses it you get there username and out it in your contact list ,so you know when they are online ,and you can send them instent messages ..i haven't use it for a few years and never used it that much ,but my daugher uses it all the time to chat with her friends .It has lots of features check msn site for more info
http://messenger.msn.com/

4.7 is the old version. It no longer works (due to new authentication protocols), but I have not found a way to uninstall it. 6.1 is the most recent version and works fine.

I use GAIM; it's mult-protocol (Yahoo, IRC and AIM too -- and more), has no advertising windows, and it's free.

To remove the standard version of MSN Messenger, I used Tweak XP Pro. Its a neat little program with lots of XP utilities, not sure how it does it but it does it.

Alternatively you can try this link

http://www.pchell.com/support/removemessenger.shtml