MSN Messenger 5.0

What is the difference between MSN Messenger 5.0 and version 4.6? The link http://messenger.msn.com doesn’t seem to specify the version but if you do a google search on it, you can download it from other sites. Is this legal? Why is it not on the MSN site? What are the advantages of having Messenger 5.0?

I have 5.0 (got it with MSN 8.0) and the major difference I see is that you can surf the web with the person you’re messaging with. I haven’t tried it yet, though.