If you're planning on playing OFP online with other players over the Internet, Codemasters recommends that you download, install and use Gamespy Arcade for finding online multiplayer (MP) games and connecting to them (for alternatives to Gamespy Arcade, look here).
While a copy of Gamespy Arcade is included somewhere in the bowels of the OFP installation CD, you should always install the latest downloadable version available at Gamespy instead. If you've previously installed Gamespy Arcade on your PC, check now if your installed version is the latest.
Note that on from Gamespy Arcade download page, you can download and ad-free version for a cost or an ad-ridden version for free. Scroll down to the bottom of the download page for the free version.
During Gamespy's installation, you will be prompted as to whether you would also like a few spyware products, such as WebHancer and Gator, installed on your system. Unless you adore spyware, I highly recommend that you opt out and just say no when prompted. If you want to know more about spyware and how to find and get rid of it if it's on your PC, go to Lavasoft and read about their popular Ad-Aware product. Highly recommended!
Sometimes, even after Gamespy Arcade has scanned your PC
for recognized games, which OFP is supposed to be one of, OFP still does not
display on Gamespy Arcade's 'Installed Games' list.
To resolve this problem, click on Gamespy>Options on Gamespy Arcade's menu bar. Under Options, click on the Games tab. On the left side is a Layout area. Irregardless of whether OFP is listed there or not, click on the Browse button and manually select the OFP game EXE file from your OFP install directory. Click the Apply button and go back to Gamespy Arcade's main screen.
On the left side, under the GS logo, and gray menu buttons, there's a NETWORK button. Under that there should be a GAMES button. If OFP is not showing under the GAMES button, click on the GAMES button to reveal it and then click on the OFP entry.
If that works and you now simply have a total lack of comprehension understanding how to use Gamespy Arcade, well, that's your headache! I suggest you go to Gamespy Arcade's support page for help.