I'm not sure about Perian being a substitute for the QT MPEG-2 component.
A colleague of mine needed to view DVD MPEG-2 files with his Mac, but even though he had Perian installed, he couldn't play them even using MPEG Streamclip.
On the other hand, I had no problems doing the same without the QT MPEG-2 component, but I have Final Cut Studio and Avid, and Perian of course, installed on my machine.
He was using 10.4.11 and I use 10.5.6/7.
As Perian is free, you could give it a try first, and see if it's enough for your needs with MPEG-2 files.