OK.. First, Norton is second only to a Virus.. norton is the worst Anti-Virus you can have.. look into AVG as a free alternative.
Second, you will need to completely uninstall your game and delete the game directory off your system.
3rd, turn off Anti-Virus completely
4th, reinstall game from CD, say no to DirectX and Gamespy Arcade
5th, download and install the game patch that the mod requires
6th, install the mod
7th, in the event you installed an older version of directX recently, reinstall DirectX 9.0c from Microsoft web site.. installing older versions of DirectX on top of DirectX 9 will corrupt DirectX which is a SYSTEM component (not a game component).
8th, re-enable your Anti-Virus
9th, when playing online, you may want to disable your Anti-Virus and Firewall to reduce lag and disconnects.
Anti-Virus has the potential to corrupt game patches and mods being installed.. and even corrupt programs being installed from CD.. when installing anything on your system, it is best to turn off the active scan..
Actually for the best running system, turning off Anti-Virus all together and running it manually once a day or every 2 to 3 days will increase system performance dramatically.. Active Scan Anti-Virus can cause multiple problems.. especially norton.. their System Works which supposedly fixes system errors actually breaks a lot of what Windows needs to operate smoothely so that Norton can WORM itself deeper into your system...
Anyhow.. that is how to get your game working correctly.. it isn't the game or the patches or the mod.. it is Norton messing you up.