Also does anyone know of a tool that shows this data in it's raw form so I can prove to myself that it will be kept?
MC will show you.
In the action window, select file properties, and then 'file type info'
when you select a file, the info you see in the file type info window is the info that is actually saved in the file itself.
If I was to re-install Media Centre or was to load my music to another PC would I be able to capture this information again or will it be lost?
If you start again with a fresh library, or on a different PC, then you need to manually create the field before importing the files. MC will not create it for you simply because the tag exists in the file. If the field already exists in the library, MC will populate it from the tags during import. No other media application will be able to read the tags in the files, though some 3rd party tagging tools may be able to show you that they exist.