I too have the exact same problem with my SGSII (i9100).
Kies tries to connect, only to result in a "This device is not supported by Kies 2.0".
I tried using diffirent USB-ports, reinstalling Kies (latest version ofc.) and reinstalling drivers.
USB-debugging is off ofcourse. I also tried different languages (Dutch and English UK), I'm using stock TW 4.0 and i haven't rooted my phone.
I can drag&drop files from my PC onto my phone with simple copy/paste.
Strange that Windows (7 x64) does recognise my phone.
I can not however get Kies to recognise/connect to it.