I too had CTD's and freezes. Tried everything and nothing seemed to really fix anything. So, I started to think and do simple math...

Morrowind was released in 2002, but, was probably in development around 2000. At that time, it was using a much earlier DirectX, more like, DirectX 5 or 7. Since Fallout3 and NV use a tweaked version of the same engine as Oblivion, which, uses a tweaked version of the same engine as Morrowind, it probably uses some of the same DirectX code. Today, 2010, we use DirectX 10 or 11. Which, by the way, does NOT contain the exact code from earlier versions.

Hence,

I downloaded and installed DirectX 5, 6, 7, 8, and 9 through 9C, and, guess what? the CTD's and freezes stopped.

I don't know if it'll work for everyone, but, it worked for me, and that's why I'm posting this.

Oblivion and Fallout both use DX 9c. Same with NV, actually very few games really take advantage of DX10, and even fewer for DX11.

I believe 9.0c is backwards compatible with the earlier versions, while 10 & 11 aren't. Windows 7 comes with ten (at least that's what my DxDiag says), but I had to update my motherboard chipset drivers before I stopped getting the CTDs I was getting - I had already installed 9.0c for other games, including this one.

All I'm saying is, it worked for me.

DirectX may be backward compatible, but, after installing older versions of it, other old games now work which didn't before, like, Baldur's Gate I & 2, Deus EX, and a few others.

I actually manually installed the 9.0c DX version that comes bundled with Fallout 3 and got no resolution with it. I don't believe its a Direct X related issue.