I think 2.4 is a minimum and even if it does run it will run like crap
Even if I tone down the textures and add a frame rate cap?
It'll probably run very poorly, or it may outright refuse to autorun when it detects your hardware settings (happened to me because it didn't think a quadro was a proper video card, I found a workaround eventually).
Depends on several factors.
First, do you have enough extra ram? Having more than the minimum is helpful. Second, do you have several programs running in the background? Closing unnecessary applications during play is VERY helpful, since you dont need things like Yahoo Messenger, your internet bandwith meter, your social network notifications, etc during play. Closing all non-essential applications makes a huge difference even if your system meets the requirements. This also means NOT using alt-tab to check this wiki during play IF it causes a slow-down.
Most important factor you can control is your video card. Having a 512mb or 1gb video card makes the biggest difference of all, since the game is very graphically intensive. Sure, you may still have to tone down textures or detail levels, but if your card is powerful enough, it will run.
My cousin runs both FO3 and FO:NV on his system, and it is a 1.8ghz with 2.5gb ram and a 1gb Nvidia 9500gt. Runs perfectly fine with just a couple textures at a reduced level.
Hope that helps.