It's possible that if you have Parallels or Fusion you could run Snow Leopard in a virtual machine. Note that Apple wants people to move forward, so they have never supported earlier operating systems than those that their Macs ship with. If you are concerned about compatibility, etc. I'd just wait a few weeks and get the Air later. In the meantime, initial bugs, etc. with Lion will be fixed, and problems with the Air may be identified and fixed. Remember, there are always bugs with any new hardware release, even if the OS is the same. The Rev D needed a few firmware updates to take care of crashes when waking from sleep, for instance.