How to Run both Snow Leopard and Mountain Lion?

[parbar]

I want to be able to run Snow Leopard and Mountain Lion simultaneously.
I have a MacPro running Snow Leopard with 2 internal hard drives. It also has Parallels on it to run Windows.
I have old programs I wrote and others wrote that won't run on Mountain Lion.
What's the best way to run Snow Leopard and Mountain Lion at the same time?
Or...is there another way to run the older programs in Mountain Lion?

 

[MichaelLAX]

Why do you want to run Snow Leopard concurrently with Mt. Lion?

If the answer is to continue to run your PowerPC apps, you can install Snow Leopard Server into Parallels

[click on image to enlarge]

 

[benwiggy]

I have old programs I wrote .... that won't run on Mountain Lion.
Or...is there another way to run the older programs in Mountain Lion?

Can't you recompile it in Xcode for ML?