1) Uninstall your device drivers for your phone. You can do this in Windows 7 by plugging your device in and going to Control Panel > Hardware > Devices and uninstalling the SAMSUNG_android. Once this is done, unplug it and plug it back in. An attempt to install the drivers will be made and the ADB one will most likely fail. Double click the SAMSUNG_android to bring up the properties for this device. Click the 'Hardware' tab. Click the 'SAMSUNG Android Composite ADB Interface' and hit properties. Then Driver > 'Update Driver'. Then select 'Browse my computer for driver software'
2) Download the drivers here: mediafire.com/?t9koyznu5ryygyt and extract them somewhere. Point the driver installation wizard to these drivers with 'Browse'. Hit 'Next.
Congratulations, your drivers are installed! Have fun rooting your Vibrant. I recommend the one click rooter, although it is just a copy of the update.zip and reboot function.