Sounds like you're talking about two different processes. For video editing there's always Adobe Premiere, although it is, of course, a bit expensive.
Then, for creating MPEG2 files, I strongly suggest using
TMPGEnc.
What is the application? Are you trying to make VCDs or DVDs? If so, then conversion using TMPGEnc is the best method, IMO. Plus, it's free.*
Actually, what kind of editing are you talking about? Are you talking about making cuts in your video? If it's an MPG file already, TMPGEnc can do that, too.
I guess we need a little more info.
*TMPGEnc is free unless you are creating MPEG2 files. that requires a license, so you have to pay for the program, but it's not expensive and the product is really worth it.