Blender has settings to render your footage correctly. I don’t know where you’re getting that 0.9091 number from, just use .9 in future computations. In Blender however just use the NTSC render setting, it’s all set up already. Just make sure you’re progressive to match your footage.
I don’t think you have to worry about that 23.976 rate either Again, where are you getting these numbers? 23.976 is unnecessary. Just render at 24 fps and import into Vegas.
If for any reason you’re still getting aspect ratio problems, render your scenes at 720x540 (with your aspect XY at 1:1) and tell Vegas you’re importing square pixel data. Vegas should correctly adjust it to non-square.
When mixing live footage with CG, you should emulate video noise (assuming of course, you’ve rendered photorealistic CG, and it’s worth the process:-). I’m not sure how to do this within Blender, but if you have sufficient compositing capability in Vegas (and I’ve read that there is), synthesize a color noise layer using a 50% gray still image at a noise level consistant with your video noise (inother words, add a noise filter to your 50% still layer and adjust to match). Give it a mild blur to match your video noise fiffusion, then apply the layer with an OVERLAY transform on your CG footage. Adjust the noise layer density to match the video noise.
Just a blind-ass guess, but Vegas probably adjusts the video to square pixels so it displays with proper proportion on your computer monitor. So… it’s still working with images at 720x480, but you’re working in the smaller area.
That’s your problem right there. D-1 PAL is 720x576. Measuring the letterboxing on DVD’s isn’t going to help you much at all, because the final resolution is going to be either PAL or NTSC to play on a television. “Standard” film aspect is supposed to be 16:9, but that’s not hard and fast, as you noticed.
A quick google will give you this site, which is pretty informational. Most DV and miniDV cameras that I know about shoot to a D-1 standard (NTSC & PAL), but this site should explain most of this for you.