Content with leaving the digital management up to consumers, the Bethesda blog notes that SecuROM is only present in the PC version of Fallout 3 to verify the game disc. "We do NOT limit the number of installs. We do NOT use online authentication or any other SecuROM functionality except for a disc check when you install the game and when you launch the game." The post further reads, "We do not install any other programs and we don't have anything that runs in the background while you're playing the game."
If you're still having trouble launching the game, Bethesda suggests you run "setup.exe" directly off the disc. Also, make sure you put the disc shiny side down in the tray. We make that mistake all the time.