I was also able to upgrade my wifes phone to 2.2 on my Windows 7 64-bit machine. The main problem that I think a lot of people are having with the upgrade is that one version of the instructions does not tell you how to upgrade it properly when there is an update to Kies Mini.
1. Make sure your phone is in USB debugging mode for the upgrade. It just works this way.
2. Uninstall Kies and then install it again. After you install Kies, DO NOT open Kiee, but connect your phone to the computer via USB and let it connect. Make sure that your phone is connected and your computer recognizes it in the device manager. Turn off your phone, remove SIM and external SD, put battery back in, hold the volume down and volume up buttons and then plug in the USB cable into the phone. Hold the buttons until a yellow Downloading screen comes up. Let the drivers load on your PC and confirm that your phone is recognized by device manager again. Disconnect USB and then take the battery out of your phone and put it back again. Do all of this before opening Kies Mini for the first time. After you open Kies Mini for the first time, it will install new updates to the Kies software that overwrites the drivers that are needed for a successful installation, so that is why you have to do all of that before you open Kies. Power on your phone, open Kies, plug your phone in and upgrade.