[Zope] Nightmare - Locked myself out (with SiteAccess). How to get back in ? back in ?

Being the silly bugger I am, I put a SiteAccess Rule into the root folder of my development Zope server and now can't get back in at all. Is there any way to force undo the last change ? I've tried deleting the 'access' file or setting its contents to 'admin:' with no password but neither succeed. This is on NT. To say that I'd be extremely grateful for any help getting back in, would be a vast understatement :) chas