Installing Snow Leopard on external HD from Lion?

Hi guys,
I have a friend whose got an older MacBook and her hard drive crashed. It can’t have Lion loaded on it and she needs my help. I’m using a new 2011 MacBook Pro with Lion installed. I have Snow Leopard on an external thumb drive – I put it on there correctly. I bought my friend a new, blank internal hard drive and have it hooked up as an external. Now, when I want to install Snow Leopard on that blank hard drive it won’t let me. It says I’m running a newer version. It doesn’t realize that I want to install Snow Leopard on the external hard drive which will effectively be the internal hard drive on her old Mac. Old Macs before 2009 won’t allow Lion.
Anyway I can put Snow Leopard on that hard drive?
Thanks
Answer #1
Can you not just install it from a flash drive whilst the hdd is in her MacBook ?
http://www.maciverse.com/install-os-x-snow-leopard-from-usb-flash-drive.html
maybe I have misunderstood you somehow ?
Answer #2
It’s okay, I have figured out an easier solution. Apple doesn’t seem to recognize that sometimes people just want to install an older version of their software onto another hard drive for other computers. The simple solution was to clone an older MacBook’s hard drive. Then install it in the other old MacBook. I told my friend that it’s just easier to buy a newer computer instead of trying to keep the old ones of life support. Oh well – it works out in the end.