Hi freitasm,
You can login to adCenter Analytics via http://adcenter.microsoft.com/. If you have an adCenter account, then you will see tabs across the top after you log in. One of those tabs is named "Analytics;" that's the tab you want to use in order to access adCenter Analytics.
If you don't have an adCenter account then after logging in you should go straight to the Profiles | Users screen.
Thanks,
-D
Darrin Wood | Sr. Product Manager, Analytics
Microsoft Advertiser & Publisher Solutions