In the empeg or on disk? In the empeg if you use jemplode you can select all the tracks with one source, choose "Properties" from the edit menu, and set an artist, source, and as much other data as you know for all the tracks.

On disk, get a batch tag editor. I use linux, so i have a command line tool called id3v2 and a perl script, and a tag stripper called mp3strip (I think).

I use augmented cddb format data as metadata for tagging. If you use linux I can give you scripts which take a table of contents from cdparanoia and download a cddb file, another to augment it, and another to invoke id3v2. They're around... somewhere.