Head back to the AOLServer site and download the source distribution, expand this into your ~nsadmin dir and try making the postgres driver again. (What I usually do at this point is make a copy of my existing ~nsadmin dir, prior to expanding the source dist., make the driver then replace the ~nsadmin dir with my copy. Just keeps the directory to a minimum).
I think this has been mentioned before and was noted that it had been requested to the AOLServer team to try and inlude the source files in the binary distributions in the next release.
Hope this helps.