Here is a modded D3D9 DLL which improves Fallout New Vegas performance for those using ATI cards.
Description: "Fallout decides its render path (how it does the graphics) based on two things. The first is the name of your videocard. This is an incredibly bad idea for a number of reasons; Fallout tends to guess information about your card wrong because of this. This DLL lies to Fallout about what card you have, resulting in much better performance with no visual quality hit (unless you're unlucky or Fallout hates you).
The other thing it bases its decision on is something internal to the DLL; since I'm not the original creator I can't say what else it tells Fallout. From what I've read, it tells Fallout's FaceGen system to use a certain method that generally works much better for everyone."
You can download it at NewVegasNexus:
http://www.newvegasnexus.com/downloads/file.php?id=34970