I want Win7 taskbar to display number of buttons combined under 1 group by the way it is done in WinXP by default - there is a number of buttons and then the name of group, while in Win7 there is only the name of group...
If I get this correctly you want the number of grouped tabs to be displayed.
There is no way you can do that through win 7 taskbar settings..
This article from Lifehacker shows settings, shortcuts and a probable solution for you: reverting back to XP style taskbar.
In here Microsoft helps you customize how taskbar groups tabs, which might be alternative for you.