Re: Pure video = VDPAU ?
Surprise, the replacement 8400GS card worked when plugged into the Dell Dimension XPS, using latest nVidia drivers (and windows XP).
I tried plugging it back into the Dell Precision 340. I managed to cure the strange power management behaviour by turning off some options in the BIOS (maybe using S1 instead of S3 did it).
But the problem remains - the system gets to the point where grub has is loading the OS and the message "Starting up ..." appears, after which the graphics mode should get enabled, but instead the system freezes in the text mode.
And with the card in, I can't enter the BIOS - pressing F2 in the BIOS splash screen results in a blank screen & frozen computer.
Same happend when trying to use a live CD - I tried knoppix and Linux Mint. Doesn't get past the ISOLINUX text message.
I managed to salvage an xorg log from when the 8400 card was fitted, and when using the failsafe xorg.conf. It reads exactly the same as the log for when the 6200 was fitted, except it cuts short (files are attached). It looks like it was perhaps trying to set a graphics mode and refresh frequency on the monitor and failing. Strange that an older 6200 card could manage this Herculean feat, though.
Any clues from the logs?