Win7, IE8, Middle mouse button - no longer opens a new tab

Hi, just upgraded from Vista Home to Win7 Home - all went well.
Using IE8 (and also Firefox) in Vista, my middle mouse button/wheel would open a URL in a new tab.
Now in Win7, I get the 'flip' function.

I'm sure I never configured my mouse button to do anything in particular when I had Vista - it just used to work and open a new tab.

So, in the Win7 control panel I've found multiple options to configure my MS Bluetooth 2.0 mouse middle button... but which option will perform the function of open a new tab ?
I know that CTRL-Left Click is the function I want but this can't be mapped to the middle button.

Any suggestions ??

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