Some suggestions...
1. Windows XP or Vista always works better than Windows 7 but if that is your only option then we have no other choice.
2. UN install all Samsung drivers.
3. First try making a connection to your device without any drivers installed. Your computer may try install some windows drivers to make the connection, that is fine.
4. Next once your device has connected then go ahead and install the Samsung drivers. First without the device connected, then plug in the device with debugging enabled and allow the computer to finish installing the drivers. This could be fast or it could take 5 or 10 minutes to complete.
Try different ports, different cables, eventually you will find a combo that makes it work. If your using windows 7 then it will probably be a bit of a battle since windows 7 just doesn't like to be toyed with when it comes to phones and drivers.