On Pete Dowson's page, scroll down to FS2004. Click the FSUIPC 3.82 link and click Save, then save it to any convenient location. When the d/l finishes, open the zip. You'll see several files, but you only want one for now. Drag the FSUIPC.dll file into Flight Simulator 9\Modules folder and start FS. Any files requiring an "unregistered version" of FSUIPC will work as long as that module is there. If you want more functionality, you'll need to register it. The documentation included with the download will tell you how.