Make my iCloud @me.com email my primary Apple ID
Have you added the @me address to your existing apple Id?

You should then be able to verify the address and set as primary address

Once it's added, you should jut be able to use it as your Apple id login

Edit: it seems the My Apple Id page has changed recently, you can no longer set an email address as a primary email address and as your AppleID.

Apple Knowledge Base article from October 2011 shows hows to do this but this ability is not present in the current live My Apple ID page.

It is still the case however that @me.com email addresses are valid aliases for your AppleId and you can log in to any service with one instead of your primary.