No, the "obay" php script doesnt need to be used with phpnuke at all. If you downloaded it and read the "read me" you could see that. All you need to do is download the obay phpscripts, upload it to your server or your host, whichever. Create a mysql database called "obay", chmod all necessary files/folders and edit the config.php file. Then run the install.php script and everything should auto install then use the /obay/admin.php script to admin the website. Im sure it is pretty easy to integrate it into and exsisting website too with a little modification.
On a side note, and Im not picking on you, In general I have found that no one wants to do the dirty work. No one wants to read. All that needs to be done is a little reading and research and it is easy to find what your looking for and find answers to questions that that person is asking. In the past I have had persons that Ive helped to set up phpnuke sites and they all ask the same questions. "I cant configure the config.php right, can you help". Then I ask, did you read through all the directions and the "read me" file? lol, the reply is always no.

Again, Im not picking on you its just the conclusion I jumped to.
voo