What sort of MPEG files -1,2,3 or 4? Audio or video files?
Photoshop 7 is old. Photoshop 8 (CS1) works fine on Leopard.
Photoshop 7 is entirely PPC code and will not run on Lion under any circumstances.
There's no such thing as QuckTime 7.6.9 -at least not publicly.
7.6.6 is the latest version and Tiger doesn't qualify for it.