To link your other Hotmail/MSN email address, please follow the steps provided below:
1. Sign in to http://account.live.com/ using your primary email address
2. Under Account Overview, below Other options, select Linked IDs
3. Click on Add Linked ID. You will be directed to the Verify your current information page. Re-type your primary email account's password. Then, enter your the Windows Live ID you want to link. Click the button Link.
Once finished, to access the linked Windows Live ID using your primary email address, follow the steps below:
1. Sign in to primary email address via http://www.hotmail.com
2. Then, on the upper right hand corner, you'll see your name with an arrow pointing down, click on it. And then, click on the Windows Live ID you added to switch to the other account.