how can I install Rosetta on IOS 10.7.5?

not possible. Rosetta support was dropped when 10.7 was released. You need 10.6 or prior.

Depending on the type of computer you have, you will need to either install Snow Leopard on a separate partition, or use a program like Parallels or VMWare to run Snow Leopard as a virtual machine.

There are two reasons why people want to: "install Rosetta on IOS 10.7.5."

1. To run PowerPC apps; or

2. To install Final Cut Studio 2 or Logic Pro 8.

If your reason is #1: either install Snow Leopard into a partition on your HD (or an external HD) to allow for dual-booting, if your Mac will boot SL, or install Snow Leopard Server into Parallels 8 to run PowerPC apps on Lion or Mt. Lion.

If your reason is #2, many people on this forum used to recommend to install Rosetta from a Snow Leopard Install DVD onto your Lion Mac: DO NOT DO THIS! Recent reports of some of these people experiencing strange system occurences and crashes lead to the conclusion that this attempt was ill advised.

There are two safe methods to install these programs:

Pacifist; or

Jeremy Johnstone's use of Terminal to install FCS2:

http://www.jeremyjohnstone.com/blog/2012-03-11-installing-final-cut-pro-studio-2 -0-on-mac-os-x-10-7-lion.html

Just out of curiousity, what was the PPC app?