Windows XP Explorer

You can add information by right clicking on an unused column in Explorer, you will get a popup menu with a lot of choices and even More.

I know it's not what you asked for, but I would recommend to add information to media/music files in a software/player like http://www.foobar2000.org.

They can get the standard song infos from a internet database and you can expand the information as you like. Even lyrics are possible and the sort and search options for your songs are great.

Also it is a good way to mix different format like mp3, flac,ape, because they all attach song information a little different.

kpax77, What you are describing (by reading the article), is exactly what I want but am not technically qualified to do all that the article calls for.  I wished that they would have allowed us to input whatever data we wanted to in at least two or three of the columns.

What data you want to add for example?
Note that the information you want to be displayed in the columns must be standard information and must be supported by the file types you have.

You could look at Audio Shell http://www.softpointer.com/AudioShell.htm

and

Infotip http://www.contextmagic.com/audiotag-editor/  The last isn't an editor but a viewer of the metadata in the file.

See my notes -  Don't know why but my comments did't show up here.  What I said is that I figured it out.  Actually quite simple.  Right click the song file/properties/Summary and WOW. Now you can use many of the categories.

Good to hear you found it, but your question was quite confusing because you asked about Windows XP explorer :)
But adding extra tag info is already explained by other members here, There are also some software out there to tag a lot of MP3 files in batch. Using file properties may be time consuming.