I have gone through the Decomb500 tutorial and now know how to determine field order and other parameters.

How do I set the field order with Decomb (not Decomb500)? I'm using Avisynth 2.5.

Also, what bearing does the field order choice in TMPGenc have when running an AVS script?

If you use an older Decomb (version 4 that is), you don't need to specify the field order IIRC. However, it's very highly recommended that you use Decomb 5, Don released a new version (v5.1) a while ago. Decomb 5 is better optimized and smarter in every way.

With Decomb 5, you'll specify the field order in Telecide by the "order" argument, like this: Telecide(order=0) or Telecide(order=1). The former means bottom field first and the latter top field first. FieldDeinterlace doesn't need the argument.

EDIT: And what comes to TMPGEnc, the program will show a tooltip if you leave the mouse pointer over the field order window for a while. Mostly it's needed when TMPGEnc deinterlaces or IVTCs the video - but most importantly if you encode as MPEG-2 interlaced, the field order must be correct or else you'll get nasty artifacts and jerky motion.

Also, what bearing does the field order choice in TMPGenc have when running an AVS script that contains the Telecide() function?

I believe none. If the source you feed is not interlaced as it isn't since you used Telecide on it, and you don't IVTC or deinterlace it in TMPGEnc for the same reason, the option just doesn't apply to anything.

One more question. Just hunted v5 of Decomb for Avisynth 2.5. Can only find older versions. Where should I look?

http://neuron2.net , under 'Mine'.

"Some capture cards require a field swap"

I'm beginning to feel that I may be having a problem with this. I don't know if the PVR250 does this or not.

Thanks for the advice, as usual!