I bought a used macbook/ wiped harddrive and no startup disks. How do I get it running?

You can buy OS X Snow Leopard for $19.99 http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard

SL isn't available from Apple as a download, it's a physical disc that is the full retail version. Since you don't give any information regarding the macbook I don't know if it would run either Lion or Mountian Lion. You can check the specs for those http://support.apple.com/kb/SP629 and http://support.apple.com/kb/SP654

Both require access to the Mac App Store which requires minimum 10.6.8, so unless you have a mac running at least that version you're not going to be able to d/l anything from Apple.

I just bought a used MacBook as well. It's also wiped.

I do have a disk for my old mac -- OS 8.5. Can I just load the old 8.5 onto the just-purchased MacBook, and then log in to the Apple store to purchase and install Mountain Lion?

Thanks

OS 8.5 is for Power PC Macs. After 2006 Macs use Intel processors and the minimum for Intel MacBooks is OS10.4.6. Your cheapest solution is to buy 10.6. It will run on any Intel Mac. The 10.6 Snow Leopard DVD is in the Apple online store. You can get it for $19.99. You will need to be running 10.6.8 to access the App Store to order Lion or Mountain Lion. http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard

System Requirements for 10.6:

• Mac computer with an Intel processor
• 1GB of memory
• 5GB of available disk space
• DVD drive for installation
• Some features require a compatible internet service provider: fees may apply.

Thank you Frederic