HDTV resolutions are 1920x1080i (i for interlaced) and 1280 x 720p (p for progressive) while PAL is either 720 x 486, 720 x 576 or 768 x 576. The PAL resolution is the same with DVDs.
"Capturing" HDTV signal into a TV is like downloading vids off the Net. No more need for convertions. You just need a HDTV tuner and a very fast rig ala Jabba's monster computer. After removing the copyprotection flags it's just a matter of transfering. A 44min 1920x1080i HDTV program weighed about 5.1GB. I'm guessing Top Gear would be about 7GB and 5th Gear about 3GB. Needless to say this is grossly impractical for almost all.
This isnt a real good comparison but this is the best I could find. Hope you get a picture (pun intended) of what am talking about.
BTW Jabba I've seen your Top Gear - Stig Compilation.avi encode and so far it's the best looking Top Gear clip I've seen so far.

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Most of the XVid HDTV program convertions I've seen have a resolution of 624x352 @ 350MB for a 44min TV program but increasingly some encoders are now offering 1028x576p (p for progressive) @ 700MB for 44min TV programs. Either size are perfect to be stored on a 700MB CD-R, if that's your thing. Heck some encodes even come with Dolby Digital 5.1 sound but that's useless if you dont have that kind of setup.
If anyone's interested I have a Chevy commercial of the pickup convertible (the very one made fun by JC) whose resolution is 1280 x 720p. Just downloaded it cause I was wondering how it looked like. So if anyone has an ftp and wants to host it send me a PM. It weighs in at under 25MB for a 30sec clip.