BellKat: Try to run the compatibility mod, run it on Windows XP service pack 3
CompleteSoup: Sorry for my lack of knowledge on the topic but how do I do that exactly?
I see this is an old post so it might not help OP but in case anyone else finds this and doesn't know the answer:
1.) Right click the shortcut for Fallout
2.) Click "Troubleshoot Compatibility"
3.) Click "Troubleshoot Program"
4.) Click checkbox "The program worked in earlier versions of Windows but won't install or run now" and click Next
5.) Click Windows XP (Service Pack 3) and click Next
6.) Click Test Program
7.) Try the game out for a while and see if it doesn’t crash now.
8.) If you think it’s running good, close the game and click Next.
9.) Click “Yes, save these settings for this program.”
10.) Close the Troubleshooter
I was having the same problem as OP and the recommended solution worked great for me.