So, I've got a playlist with a bunch of mp3s, some quieter than others. How do I utillize the Dynamics compressor (or whatever) to have them playback at approx. the same volume?

Basically, I was under the (mistaken?) impression that Foobar 2K would normalize a playlist. Perhaps I'm mistaken. If normalization of a playlist is not possible then it would be a real nice future option.

Just track gain all files (Right click playlist tab > ReplayGain > Scan per-file track gain) and ReplayGain will do the job for you.

For albums, you'll probably want to "Scan selection as Album" so that you retain relative loudness of tracks within an album. For example, the artist may have decided that track 1-4 should be loud, then track 5 should be a softer instrumental, and tracks 6-9 should be loud again. Don't worry, album scan does a "per track" scan at the same time.

For playback, you can choose between "album gain" and "track gain" (or disable replaygain) in Preferences > Playback > Replaygain.

Ah yes, excellent! Thanks.
Foobar has got to be the most versatile music player I've yet used, handling more formats than I realised existed. Great stuff! It's not pretty but then, as I've always said: 'It's the beer I want, not the bottle'
Thanks again

You can make it prettier Check out these plugins: Foo UI Columns Foo Tunes (BETA) or Foo Looks

And yes, foobar does rock

Steve