Go to: My computer, then C drive, then Program Files, EA GAMES, Battlefield 1942, then the Settings folder. In that folder you will see a file called VideoDefault.con. You will want to double click this file to open it. If it asks you what Program to use (in Windows XP you will first want to choose "Display a list of programs for me to choose from), choose Wordpad. In there you will see a line with this command:
renderer.allowAllRefreshRates 0
Change the 0 to a 1 and then Save the file. This will allow refresh rates above 60 Hz in the game.