Usually, there is a directory where you installed PHP called "extensions" That's where the dll goes. Otherwise, do a search and find any other dll files in your PHP directory. Put it with the others.
Also, don't forget to edit your php.ini file. Somewhere in that file, usually toward the bottom, there is a list of dll extensions. There needs to be a line there for it. If it's not already there, it should be easy enough to create a line similar to those already listed. To enable a module (dll), you usally remove the semi-colon at the beginning of that line.
Hope this helps!
