If I buy a Mac that comes with Lion, can I install it on my old Macs too? Possible Duplicate:
  Does buying a new mac also get you Lion on your Apple ID?  




If I buy a new Mac with OS X Lion, will I then be able to update my old computers to Lion via the Mac App Store without charge?
No - macs ship with one license to Lion - for that mac.

If you buy an upgrade outright, that applies to all your macs.