Many people have asked for help doing this & even with detailed instructions couldn't do the task. So I am finally fed up & I'm going to make a guide to do it.
Step One :
Naturally, I would suggest opening MSN for this.
Step Two :
Go to the contacts drop down menu & click save contacts.
Step Three :
Save the contacts to any name you'd like, you'll need it later.
Step Four :
Go on your other MSN which you'd like to add the contacts to.
Step Five :
Click contacts once again & chose import contacts.
Step Six :
Find the folder which you saved your contacts in step three.
Step Seven :
If done correctly, it should say what contacts you are adding, click OK.
There you are finished, quick & easy, but I found many people didn't know how so I thought I'd try to help out the few out there.
+rep if it helped