Try this before you fastboot. Power the phone on normally and plug it into your computer. USB debugging on. Wait for windows to automatically install the drivers. After this is done, unplug your phone. Now run the pdanet installer. It will prompt you to plug your phone in. From this point, follow the installer instructions to a "T" and you should be fine. After pdanet installs, unplug your phone and power down. Now, open device manager. Boot your phone into the bootloader (three finger salute). Now connect your phone to computer. In the device manager window, you should see Samsung (something...) followed by Android 1.0 driver (or something similar). Once you see this, you're good to go. Go ahead and double click install-superboot-windows from the root of your computer's C drive. Let me know if this works.
More than likely the device is going to hang on the Google screen. This is fine, don't panic. Let it sit for 5 minutes. If it doesn't reboot on its own, now do a battery pull. Boot up normally and enjoy your superuser privileges.