Should be possible, but it isn't Plus..
1) Check the options:
a) Autologin
b) Save password
Create a new task with the task scheduler which starts MSN Messenger
Logging out is a bit harder, but you can try a cool named "Pskill" (http://www.sysinternals.com/Utilities/PsKill.html)
Should work!
If not, try "AutoIT" combined with the Task Planner
AutoIT is a scripting language which can create macro's..