According to the Microsoft article, "Exchange Server 2007: Platforms, Editions, and Versions":
"When you install Exchange 2007, it is unlicensed and referred to as a Trial Edition. Unlicensed (Trial Edition) servers appear as Standard Edition, and they are not eligible for support from Microsoft Product Support Services. The Trial Edition expires 120 days after the date of installation."
This means that you will be unable to add additional storage groups, managed folders, or use any of the Exchange Enterprise features until you enter the Enterprise product key.