a

You can block them.
You won't get anything else from them after that.

Open your MSN Messenger window so you can see your list of contacts and then right-click on the one you want to block. A list of options will come up and about two-thirds of the way down is Block.
Click that and follow instructions.
Then just delete the contact and that'll be the end of it.

Also...besides what Heliotrope pointed out...you can also check out the profiles attatched to the emails, if they have one. I did just that on them...

[email protected] shows up as Mr_mp31 from Virginia, the profile was last updated 12/9/2004.

http://members.msn.com/default.msnw?guids=5U24bFIAKE5lPV5TzcNIMvPmEJAuwRZGP76DtsqSMW4eIpxOnHqx39QrM1yCb36usw

And romance_knight_2004@hotmail shows up as a member without a profile.

These are found under the contact button on top of the messenger, click on it, and then manage contacts button, then view profile.

If you can, document the harrassment and/or abuse. MSN frowns on it - report it to them. Also, dependin' on the nature and severity of the stuff that bothers you, it might even qualify as a police matter.

The idiots that pull that sorta crap figure they're safely anonymous. They aren't. Nail 'em; they almost certainly don't expect anyone to even try to come back on 'em, and likely have done nothin' to make themselves difficult for authorities to track down.