Vista - Standard use for file detail fields?

Vista has a lot (hundreds?) of file details fields (e.g. comments, artists,
genre, ...). Some of the fields are pretty self explanatory. Some are not.

Is there a web site that defines or recommends what each field is intended
for?

I just bought a bunch of mp3s from amazon, napster, etc. I want to put the
name of the store in one of the detail fields so that at a glance I can tell
where the file comes from (bought from online store, rip from a CD, etc).

Which is the most appropropriate field for this purpose? Amazon use the
comment field to tag "amazon song ID nnnnn". However, I would like to
reserve the comment field for storing my own comment (e.g. this song makes
me laugh, instruments only, etc).