They won't go away, help please

I would appreciate it if somebody could help me. I am very computer illertate, but I keep trying.

My problem is this. I have MSN messger and decided it was time to clean up old contancts that I haven't talke d to in years. I would right click , hit delete and they would go away. That is all exept one.

They have a yahoo addy. when I try and delete them I get a box that says I can not delete them. The computer refuse s too. I also notice d that in that pop up box that there is their addy and then in parenthesises after it it says xxxxxxx@yahoo.com (.NET Messenger Service)

I have no ide a what that means and also when I try to deltelt them then it closes my MSN messgener and I have to sign back in again.

I would be grateful if somebody could tell me in baby steps what is goign on and how to get rid of them please.