Although you previously used MSN Messenger with Hotmail or MSN.com credentials, Windows Live Messenger allows you to create a standalone Windows Live account in order to use the service. You can use any valid email address to create this account, including an Apple email address with an @Mac.com domain name.
Although Windows Live Messengers, also known by its former name "MSN Messenger," is owned by Microsoft, you need not use a Microsoft email address to make use of the service. For example, register a Windows Live account using your Mac email address and begin using Windows Live Messenger once your registration is finalized.
Windows Live Account
You register for a Windows Live account on the Windows Live Account registration page. After inputting your email address and selecting a password, you enter personal contact information and then select a security question you'll use if you lose access to your account at any point. You must confirm that you own the email address you input -- namely, by clicking a link in an email message Windows Live sends you -- before your account becomes active.
Changing to Mac Address
Alternatively, if you current access Windows Live Messenger using a Hotmail or Live address, you can edit your profile to use a Mac email address instead. To do so, log in to Windows Live Messenger using your usual email address, then select "Options" from the drop-down menu next to your display name, which takes you to account options. Input the Mac email address, click "Save," then click the link in the email Windows sends you to confirm you own the address and begin using it in conjunction with Windows Live.
Disadvantages of Mac Address
When you use Windows Live Messenger with an MSN or Hotmail email address, you are able to receive notifications via Messenger whenever you receive an email message, as well as to access Messenger online via Hotmail. If you use Messenger with a Mac email address, you lose both of these capabilities.