MBA 2008 Model - Mac OS X 10.6.8 is sluggish and I want to revert back to factory settings (OS) but don't want to loose my Office for mac 2008, how?
Snow Leopard is known to be better optimized than Leopard so I'm not sure it would be that great. The main bottleneck in the original Air is the slow as hell hard drive if yours doesn't have an SSD.

Regardless, you should backup your apps and data to an external drive (USB 2.0) and then reinstall the original OS (which if I remember well came in a thumb USB drive with the Air) and then restore your data and apps from the external drive.