I have a vantec nexstar3 with esata and usb ports on it. i didn't need any drivers for it to be found in windows 7.
Is the drive you put in the enclosure new and never used? if so, you need to go into disk management and initialize the drive and format it, then it will show up in windows.
To get to disk management, click start, right-click computer, and select manage. Then click on disk management in the left pane. You should see your new drive in the right pane.