Make sure you have the BF1942 Patchswitcher. Follow the Readme's instructions to install.
(It WILL NOT work if you already have installed the 1.61b official EA Games patch!!!)
http://www.download.com/Battlefield-1942-Patchswitcher/3000-7435_4-10598803.html
Also make sure you've got the mods we play. Here are links:
DesertCombat: http://files.filefront.com/Desert+Combat+Mod+v07+Full/;2033471;/fileinfo.html
DesertCombat Final: http://files.filefront.com/Desert+Combat+Final+Client/;3667807;/fileinfo.html
Desert Combat Extended: http://battlefield2.filefront.com/file/DCX_09_Full_Client_Install;43294
Desert Combat Final Extended: http://battlefield2.filefront.com/file/DCFX;54557
DCFX 1c Patch: http://battlefield2.filefront.com/file/DCFX_Joint_Arsenal_Client_Files;54560
Install DC then DCFinal then DC Extended then DCFX then the 1c patch, in that order.
Forgotten Hope: Install part one then part two then three.
File #1: http://battlefield2.filefront.com/file/Forgotten_Hope_07_1_of_3;49588
File #2: http://battlefield2.filefront.com/file/Forgotten_Hope_07_2_of_3;49581
File #3: http://battlefield2.filefront.com/file/Forgotten_Hope_07_3_of_3;49580