This is what I did to make Livetype work on my Lion 7.3. In fact, I am running Lion 7.3 on an external hard drive and kept my original Snow Leopard on my iMac. I did not have to install Rosetta at all...
1. I drag the Livetype application to my Lion apps. folder.
2. THIS IS VERY IMPORTANT: Create a LIVETYPE folder in your LIBRARY IN YOUR LION HD (or whatever you named it) and NOT your USER (usually You or whatever you named it) - LIBRARY folder. To clarify...the user folder to library will fall under LION HD...do not create a LIVETYPE FOLDER THERE...again Lion HD or Macintosh HD - Library - Livetype
3. Start extracting your your livetype pkg. If Lion, does not allow you to do so because of incompatibility...get yourself the PACIFIST software (program) to extract and install it...but in my case I never had to use it. The LIVETYPE you drag in your application (no.1 instruction) will open but nothing is in it because you have not actually intalled it's content inside the Library folder of Livetype. Once all components are installed, open your LIVETYPE and voila, you will be able to use it again...the contents in the Library folder - Livetype folder will be empty and is now reflected in the application itself.
4. Now whether you can incorporate it with FCPX directly, that I have not tested yet...but I know I am able to use my familiar LIVETYPE app again and render and apply it to various video software that I have.
I hope this helps you and the rest of the crew. PEACE.