Currently Being ModeratedMay 5, 2012 8:05 AM (in response to tarynfromhimrod)
If you bought Aperture online, you should have received an email with the serial number - search your mail box. If you bought a boxed retail version the serial number is inside that box.
If you cannot find it, contact Apple; see this support article:
Pro Application Replacement Serial Numbers:http://support.apple.com/kb/HT1861