The pixel aspect ratio issue has been covered a few times, but here’s a synopsis.
1) Graphics programs typically use square pixels
2) Broadcast formats use non-square pixels
If you are creating stills in Photoshop or whatever for use in Vegas, multiply the destination format width (in pixels) x the destination format pixel aspect ratio.
Ntsc= 720×480 pixels, pixel aspect = .9091
720 x .9091 = 654.552 (round it up or down to a whole value, to 655 or 654)
for a still image size of 655 x480.
If you look at the project presets, you’ll see a table of pixel aspects- these will be different for NTSC widescreen, PAL, and PAL widescreen etc. Use these as your multipliers.