Then I import the mpg and the aif into DVD Studio.
But then I guess that is assuming that with FCP you also have Compressor and DVD Studio.
As for web, I think a lot of people use H.264 as their compression.
That would be:
Export, Quicktime Movie
Setting: Custom --> Should open Squence Preset Editor
Here you can compress it as H.264 and give it a custom frame size.
Hope that helps, if people have better ways, please correct me. I'm still looking for the best too.