You've hit the crux of the matter. I also got a similar cable for my i300 and encountered the same trouble. I have not found a USB driver that recognizes the I300, and have been advised that none exists. I consider it less of an issue of MS/Windows support and more of Samsung. In cell phone / PDA terms, five years is a real long time.

But don't despair, there are alternatives: You can hunt down or dust off a serial cable or charging cradle, and get a USB to serial adapter. Another user on this forum reports success with a cheap USB IR dongle and hotsync via IR. In any event, the USB cable you have is the most compact option for charging your phone.