Anyone know of a good free mp3 tagging tool to fill in my track number field for me.

Well, my favorite mp3 tagger is "Tag & Rename" - liked it enough to actually purchase it (it's shareware).
In that you'd create a pattern like "%6 - %0" to dig out the track number from the file name and populate the id3 Track# tag using the mp3 file name to id3 tag function. (%6 is track#, %0 is a dummy for stuff you wish to ignore)

"Dr Tag" or "mp3 Tag Studio" should be able to do this as well. (both sharewares IIRC, Tag Studio might be ad-based in the free version)

/Michael