I use MSN and ICQ but personaly i prefer ICQ for 2 reason 1st because is not from Micro$soft and 2nd cause u can send offline message and other's many thing but unfortunaly the most of the people use msn
SP2 do a backup of SYSTEMS FILES if you want to go back and will don't touch your's other date like u mp3, this will cost you around 500mb and if all is working ok after 2 weeks you can delete that back up from the control panel.
Myie2 use the IE engine, and have all the IE security problems.
Firefox is the more stable, fast, secure and you can customized with some cool extensions.