There's nothing like (kindof) answering your own questions with a little help from others

TweakUI did go a long way to resolving my problems - I hadn't noticed that MS download slip out to be honest!
XP Taskbar Properties has On/Off controls for Group similiar taskbar buttons and Hide inactive icons and coupled with TweakUI I can alter the threshold where the grouping takes place (if I leave grouping enabled) at least on the taskbar buttons.

After this exercise I now know exactly what it was I was really looking for, I need a way to group Explorer Taskbar Buttons by site address.

For example, this evening I browsed via 'open in new window' a lot of pages, I would have quite happily have had those pages grouped together (by site) but it was inconvenient to have ALL open browser windows grouped together.

Are there grouping variables other than simply threshold or on/off?