Here's what you need to do. Windows updates your usb drivers all the time and it sucks because it never fails to mess up the Samsung drivers. Here's what you should consider doing.
1. go to your computers control panel / add and remove software (win xp) or programs and features windows 7.
2. Uninstall Kies and Samsung drivers.
3. When complete, restart computer and phone.
Download these Drivers
4. Install the drivers on your computer but do not plug in your phone until it has completed.
5. plug in your phone that is already started. It should now recognize your phone and at the bottom right corner say it is installing the software for your phone. click on view details. Several drivers should load and as it progresses green checks will appear when successful.
Now you should be able to continue. Here is my guide to the root the AT&T Version. All required files and detailed instuctions can be found there. If you have any problems feel free to contact me through that thread. I am subscribed to that thread and will received notifications.