QUOTE(Remedial Sound @ Oct 27 2006, 13:13)

I presume you're trying to edit the artist field in the id3 tag? Or is it a different format? AFAIK id3v2 allows the "/" character. I'm not sure about id3v1 (?), so it might be that you only have id3v1 tags in your files and that the unacceptable character is being substituted with an underscore "_".
Keep in mind also that back/forward slash characters ("/", "\") are not allowed in windows filenames. If you use foobar to rename files based on your tags, it'll substitute an underscore or other acceptable character for such unacceptable characters.
Changing all the tags to ID3v2 does nothing. Still an underscore, not a backslash.