You need to follow these steps in order to use a plug-in that relies on OpenCV:
Download this additional bin folder (1.2M) containing OpenCV's dlls.
>> I recommend to place this folder next to the plug-ins, typically in "...\Adobe After Effects XX\Support Files\Plug-ins\Nabscripts\".
Add the path of the bin folder to the Path environment variable of your system.
>> On Windows XP, right-click My Computer and then choose Properties. Click Advanced tab and Environment variables.
At the bottom of the dialog box, select the Path variable and click Edit.
Now add the path of the folder, e.g. "C:\Program Files\Adobe\Adobe After Effects CS3\Support Files\Plug-ins\Nabscripts\bin"
(without the quotes and notice that the different paths are separated by a semi-column).
Troubleshooting
If AE doesn't load the plug-in it's most likely because it doesn't find the required dlls, check that the Path is properly set.
Feel free to send me an email if you have problems with the installation.