You could do lots of things.
If you still have the cd's that you got the mp3's from I suggest just deleting the old mp3 files and re-uploading them through iTunes. Kind of a pain in the butt.
You can make your iPod a drag and drop external drive. Here's the link to the how-to.
http://docs.info.apple.com/article.html?artnum=93651
You could just add the information manually to the music. More of a pain in the butt that re-uploading the music probably. I guess if you just do the albums and not the genre and all that it wouldn't be that bad.
You could just deal with it.
You could try this app if you want to change them manually.
http://www.fixtunes.com/
Have fun.