What do I do in this instance:
I'm working with a DVD (I've ripped a DVD and am working with the ripped mpg file in Vegas). According to the box the DVD's format is NTSC. When I render in Sony Vegas do I render in NTSC or PAL? I think it should be PAL as I'm in Thailand. I'm a bit confused.
You may want to double-check your ripped file format to see whether it's interlaced or not. If it is, you can most likely de-interlace it in Vegas (I don't use Vegas, so I have no idea), then render the file to whatever your playback requirements are.
What do you want to do with the finished video? NTSC DVDs are 720x480 at 29.97 fps, while PAL Uses 720x576 at 25fps. If making a new DVD, you could convert to PAL, but you'll be converting both increasing frame size and lowering frame rate, which will diminish the final quality.
My understanding is that PAL DVD players will play NTSC DVDs, having built-in conversion circuitry. You can easily verify this on your end - does the NTSC DVD play in your DVD player? If the answer is yes, then perhaps keep the workflow NTSC for best results. If creating a clip for the web, then NTSC/PAL doesn't matter, computers can play anything, but again avoid unnecessary conversions.
For the web, NTSC or PAL doesn't matter, computers play anything. Edit NTSC as NTSC so that you're not converting frame size or frame rate, then export to a web format keeping the same frame rate of 29.97 for delivery.