I've looked on riocar.org/downloads but didn't see it, and searched the BBS but only found threads reffering to it, where can I get it? Maybe it's so obvious I'm just overlooking it?
Click on the link in my signature. It's intentionally not in the downloads section because it's still a buggy program that I don't consider fit for general release.
I understand it uses ID3v2 tag info for the scroll. Which field in the tag does it use?
For lyrics, it uses the synchronized lyrics and text (SYLT) frame. A list of the fields that it supports is in the README, but the only one that you'd be interested in right now is the comment field. The ID3v2 comment field isn't limited by the spec, but the player uses the comments stored in the FIDs themselves, which they limit to 255 characters. I haven't tested it, but I believe emphatic, because it's pulling the comments out of the ID3v2 directly, does not have this limitation, so you should be able to put whatever amount of data you want in there. I will warn you that configuring the custom info modes isn't for the faint of heart. Though there are examples of them in my README, it's something you won't want to do unless you're good with the shell prompt and hand-editing your config.ini and all that stuff. emphatic also has no reliable auto-install process, except for an MS-DOS batch file that FTP's things over, and even the FTP script requires edits to put in your IP address, etc. It's all documented, but it's far from automatic.
The thing is, I think you would want to put the info you're talking about in other fields than the comments. Band members, songwriting credits, etc. all have their own fields in ID3v2, but those fields aren't yet supported by emphatic. I plan on it, though.