In f/u to a previous and distant thread, the same friend had unearthed an old ideq 220n which was a SFF nforce2 mobo with an undervolted athlon XP-M to 1 Ghz. Doing what any reasonable person would do, he installed a PCI 8400 GS card he found on sale and decided to give HD video content a go after he wiped the drive, re-installed WinXPsp3, and re-installed drivers + MediaPlayerClassicHomeCinema only.
It was amazing to see the CPU utilization at ~15-20% the whole time 1080P was playing whereas before it would drop whole minutes of HD video with CPU pegged(even when clocked up to 2.2Ghz). We only saw 1 video, so we'll see if it holds up to other videos as well.
In short the 8400GS has it goin on with HD material.