yes once you have windows live messenger and messenger plus ... just select "allow multiple accounts"(or something like that) during set up and your away
well technically you could if you had 2 different versions of msn or 2 of the same versions running simultaneously theoretically its possible to do but you might need some kind of program to help support and run it. because it might cause allot of errors and stuff basically you would get the same program colliding because they are all run with the same commands but yes its possible
lock in? Do you mean login the same time? Well, you can use 2 or more different msn accounts but you need to use "3rd party" clients not the msn messenger. Use trillian or pidgin.