half life 2 and my sammy dlp...no 1280x720  

i have a hlp4663w and i cannot get half life 2 to run in 1280x720. when i put my 19" crt in 1280x720 and load the game, it loads up fine. i have windows res set to 1280x720 and try to load the game, no go. i've tried going into the game, changing the res over, exiting to windows and then loading the game back up....no go. no matter what i try to get the game to load while on my dlp tv i get an error message saying "game cannot load the current resolution and is in safe mode. game will try to reload" (can't remember the exact words but it was something like that). it keeps giving me that error and trys to restart and nothing happens, it just keeps trying. but it will load on my crt. i have a radeon 9800 pro and i use dvi to hook up my tv. can someone please help me get this on the road as i really want to play the game in 46" glory. thanks.