Clart - they aren't available on a lot of the smaller maps. I think
all of the 64-player maps have planes and choppers in them (though I could be wrong) and if you play on single player, you normally find that the bots nab them first before you get the chance.
Flying choppers is quite easy compared to the older Desert Combat - those took real skill. If you have a 3-axis joystick such as the Microsoft Sidewinder FF Pro, flying them is even easier. Granted, the transport choppers are more of a barge to fly than the Cobras and stuff, but at least you can transfer several guys into the landing zone with you. You even get ribbons, badges and medals for doing the job of troop-taxi-driver!
And for those people who don't like going online, I cannot recommend the following Single Player mod highly enough. It's not even 8MB, but raises the current 16-player single-player game limit up to 32 - 31 bots plus yourself. Proper carnage on some maps!
http://totalbf2.filecloud.com/files/file.php?user_file_id=39650
D.