hey guys new to the forum and need some help, basically installing NV on my new system, (which can run the game easily enough,) i am running it through steam (but i cant register it because i lost the keycode >.<) and whenever i click play it goes to fullscreen, goes black, and the crashes with the message 'Fallout NV had encountered a problem and needs to close. sorry for the inconvienience.' i have tried multiple ways to fix this but nothing has worked, and i am really getting frustrated now, can anyone help? here are my system specs.

windows xp home SP3
3Gb DDR400
250gb HDD
dual core 2.4ghz processor
graphics card i cant remember but it is way above minimum spec.

PLEASE HELP!!! QQ

Post a dxdiag. http://www.gamesas.com/index.php?/topic/1122570-how-to-dxdiag/
Use spoiler tags. Top left of the textbox window where you type your reply above the bold/italics,underline buttons. Drop down box is labeled other styles. Select spoiler and just click add.
Then paste your info between them. This is also outlined in the how-to.