Ok, then assuming you have a modeline with no "vsync" or "hsync" parameters, does that force vertical syncing off?

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Currently running: R5.5, HD5000 x 2, PVR150, Athlon 64 3000+, Chaintech VNF4, 1GB RAM, 2 x 250GB in LVM, MSI NX6200TC -> AA 9A60 -> HDTV

I don't understand what you're trying to do. Your TV set requires a signal to sync it to the signal from your video card. No sync = no picture. It needs both a vertical sync and a horizontal sync. The "sync using openGL" feature is supposed to line up the even and odd fields of the interlace display (I guess) but it doesn't seem to work very well -- or it adds too much processing.

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How do you know if you need a -vsync or a +vsync in your modeline?

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Currently running: R5.5, HD5000 x 2, PVR150, Athlon 64 3000+, Chaintech VNF4, 1GB RAM, 2 x 250GB in LVM, MSI NX6200TC -> AA 9A60 -> HDTV

I also upgraded to the new driver and it seams to be working pretty well. Though I did upgrade because I thought the driver was the source of some video noise (scan lines moving diagonally across the screen). As it turns out it was the output from the MX440/MX4000 card. When I switched out the card and replaced it with a 6600 GT the stuttering actually got worse and I had to turn on XVMC. With the MX440 I could actually watch HD without xv.

Apparently there is a known issue with the 6600 card or just the 6 series cards and smooth playback. I plan to go back to the MX440 but the picture quality just looks better with the 6600. The MX440's are cheap right now so I might just buy another and see what happens.