Stuck without admin account on a MacBook Air running 10.5.8
Learned something new today:  You can break the firmware password with help from Apple.

http://reviews.cnet.com/8301-13727_7-57542601-263/efi-firmware-protection-locks-down-newer-macs/

This note says that Authorized Service Providers are equipped for that?  http://support.apple.com/kb/ts3554