Hi,
Please click the link below for the SCE 2007 licensing information.
System Center Essentials 2007 Pricing and Licensing
http://www.microsoft.com/systemcenter/essentials/howtobuy/default.mspx
For licensing questions, you can call 1-800-426-9400 (select option 4), Monday through Friday, 6:00 A.M. to 5:30 P.M. (PST) to speak directly to a Microsoft licensing specialist.
Note: If you are outside of the United States and Canada, you can get pricing information from your local Microsoft office. Find contact information for your Microsoft office on the Microsoft Worldwide Information site.
Hope it helps.
Sincerely,
Yog Li
Microsoft Online Community Support