Not sure if this is just me, but:

1. I don't think when I edit the tags on Amarok the tags display in iTunes. Yet when I do it on iTunes or EasyTag the tag stays on and appears on Amarok. Does Amarok's tagging only work on Amarok and doesn't write into the metadata?

2. When I use the "Fill in with MusicBrainz" feature for the tags it says it can't do that for MP3 files. Does this feature only work for OGG?

Can these problems be solved with plugins?

Thank you for any help.

As answered many times in various places, amarok writes id3v2.4 tags. Not sure what itunes sees (can't say I've ever had a problem with amarok-edited tags showing in itunes), but easytag can only read/write up to id3v2.3 due to a different tagging library being used.

Sounds like you might be missing a library - possibly something libtunepimp needs, maybe libmad?

What you need is the libtunepimp3-mp3 library. That's the name of the package for me ((K)ubuntu Edgy), you may need to look for yours. Search for libtunepimp or musicbrainz.