If you have the originals, you better rip the original audio straight to mp3, since converting from ogg to mp3 makes the sound quality worse. But as many people do not have the originals (sooo much legal mp3 files without original discs, hmm..), you'll just probably have to bear.
Can't oggtools decode ogg to wav? If it works (as I believe it should), then just use lame or some other tool to recode wav to mp3. And since clever people automate big works with scripts (or something), write a nice script that will do it automatically for you