i installed directx 10 and didnt work. System:
Microsoft Windows XP Professional Version 2002 SP2 32-bit
Intel Celeron CPU 2.80 GHz 2.81 GHz, 1.50 GB of RAM, ATI Radeon X550
i tried to starti it: From DVD, From Launcher, 2 click on exe....
black screen then back to desktop.
AHH I KNOW WHAT IT IS: FKIN VIDEO CARD Q.Q

Actually, the CPU is also below the game's requirement. Celerons simply aren't / weren't intended for game playing, and yours is already rather elderly, I don't think that I would bother investing any money in CPU or GPU upgrades for that PC.

Incidentally, there has never been any official Dx10 for Windows Xp, only for Vista, but Fallout 3 happens to be a Dx9 game anyway.

Gorath