What does 'offset' mean anyway I noticed about half of my collection is '0' the rest rather large numbers?

Offset is beginning of actual MP3 stream (I don't know units - bytes?). Those with large offsets probably have ID3v2 tags prepended to them. See r3mix.net for a rant against ID3v2 tags, and Mark's utility for extracting and removing them.

and Mark's utility for extracting and removing them

Is there a utility your aware of that runs on Win 98?

Many. I use MP3 Tag Studio (mostly to set both ID3v1 and ID3v2 tags in controlled manner, but it can also remove them.)

I have been using MPTagger, I had used MP3 Tag Studio v1.61 until I changed every single one of my 800 files to the same thing accidently, big mess. I'll see what the new version has to offer.

I had used MP3 Tag Studio v1.61 until I changed every single one of my 800 files to the same thing accidently, big mess

... and didn't notice untill it was too late for undo, eh? Undo did save my hide once or twice

Uh yes. You have to really goofproof things for me at times, even 'undo' needs a 'undo'.

OK does the 'offset' really matter much in the bigger scheme of things?

No, not really. I suppose empeg 'writes it down' in order to skip over tags (as opposed to waste time and cache by reading them), so the difference is a single seek call. Also, unless ID3v2 tags contain something as extravagant as hi-res scan of CD booklet, they still use only several kilobytes. As I said in another thread, I still think it is a good idea to keep ID3v2 tags, provided one tidies them up for one's own use.

I have been using Winamp to copy the v1 info to v2 but I have a long way to go to do all my files, a long way.

Wow! You've got a lot of patience! I simply use Tag & Rename, a VERY good utility. Great at doing 'batch tagging'

Give it a go, I'm pretty sure you'll like it. (I liked it better than mp3tagstudio because in the days I started using it, mp3tagstudio didn't do v2 tags yet)

Theres a fully-functioning one-month trial version downloadable from the site.