I had issues using Kies and windows xp and wanted to share what I had done. Just got my my player in and it's the non-US version (Samsung Galaxy S Wi-Fi 5.0).
I tried what most had said about switching debug on/off, connect disconnecting but nothing worked. I was looking the the setting menu and under USB Management, there was an option under Wireless and Network > USB settings and there are 3 options - Samsung Kies, Media Player, Mass Storage. I picked Samsung Kies and reconnected and it worked.
I realize this might not be an option available since this thread is for the S2, but thought I'd share in case anyone had any luck.