ok found a fix for you and im sure its the same issue so ill write it up when i get home and add it to the FAQ as this deffo works
go into device manager and uninstall absultely every samsung usb related driver including the ADB
if it gives you an option to delete it click yes
after all of the drivers are deleted, DO NOT connect the device and make sure you reboot your machine
once you boot back in connect the device, windows 7 will try and auto find the drivers so click skip and it should fail.
click
here and download the samsung usb drivers
extract them to a folder (default file name is good so you know which drivers they are)
go into device management and right click samsung usb device. click update driver, click browse computer for driver software, click browse and point it to the driver folder of the file you just extracted.
windows7 should install samsung galaxy usb composite device and then it should start auto installing the rest of the drivers
It will now fail on one driver and should show in device manager as unknown device
now this is the ADB driver.
go to device manager click update driver, click browse computer for driver software, click let me pick, click all devices, click have disk, point that one to the usb_driver/amd64 folder you downloaded from yardimage and select samsung composite adb interface.
jobs done