I installed MySQL 5.0.18 and not my banner ad program does not work, for some reason it is not compatible with MySQL 5 so can I go back to MySQL 4.1.18, I tried but I get a PHP stack error. Can this be done or do I need to wait for the ad program to update
The most likely problem would be some kind of api change. You might be able to isolate the Client library files that are required, and make sure those are loaded. I think all you need is the libmySQL.dll, but I haven't tested.
You should be able to connect with an earlier version, just don't use the newer features.