Installing Lion on a separate partition in Mountain Lion

I want to upgrade to Mavericks but my (old) version of Pro Tools won't work with it and I don't want to upgrade.

So, my solution is:

1) create a new partition

2) install Lion (or maybe Mountain Lion) on it.

3) use that partition for Pro Tools and upgrade my other partition to Mavericks

I need some advice on the process though.

I've done #1, and I know how to do #3, but #2 is giving me issues. I downloaded Lion from the app store but when I try to start the installer it says that "This version of Mac OS X is too new to run "Install Mac OS X" from Mac OS X 10.7."

So do I,

1) put Lion on a thumb drive and hold down the option key when I start the computer to boot from it? And if so, will it let me select the partition to install?

2) I have a disk for Leopard (10.5.2) and if I put that in it gives me the option to restart and begin the install process but I don't want to do so unless I know it will let me select the right partition, will it? And I'd really prefer to run Snow Leopard, Lion, or Mountain Lion for Pro Tools. Snow Leopard is actually the last supported OS for my version but it has worked fine on Lion and Mountain Lion.

Any guidance is appreciated. Thanks!