Windows fields compatible with iTunes

Hi. I use iTunes for my music database.

I've used most of the popular fields already - but I need to add one more field, which is cabale of taking 8 or 9-digit entries, mixed numbers/letters

in iTunes I can see that I still have the following empty fields capable of being used:

Episode ID
Sort Name
Sort Album Artist
Sort Album
Sort Show
Sort Artist
Sort Album (not sure if they are already in use)

can I sue any of those fields and then make them accessible through Windows?

OR can someone suggest any other way of adding a field I can use in Windows too?
(I already use all these: Name, Artist, Album Artist, Grouping, Composer, Comments, Genre, Year Track Number, Disc Number, BPM, Description, Sort Composer)

see the help on supported fields:
Please note that there is an extra column for iTunes.

thanks for quick reply. will check it out asap

quick question: does the fact a file have ID tags mean it's automatically saved by Windows?

for example, when I go to an MP3's properties > details in Windows, many of these tags aren't visible - so if my computer crashes will I lose data that I cannot see in Windows?

I just want to know that if I start entering data into, say Sort Album Artist, which has an ID tag but is NOT visible in Windows, is all the data saved as soon as I back up the file?

hope you understand my meaning, cheers

If you enter data with MP3tag then all the data is attached to the corresponding file as a "tag". The data like ARTISTSORT becomes part of the file.

Some players tend to store metadata only in their proprietary database and not to write the data to the files. But with MP3tag you are on the safe side. The data is where the file is.