Interesting.. When playing back 1920x1080 video, my Geforce 6800 Ultra (with broken HD video coprocessing,on a P4 2.8 @ 3.73) dropped frames. On an Opteron 165, my Geforce 7900GT (with working HD decoding assist) doesn't drop frames. Naturally, I assumed that a Geforce 4 MX would be even worse at HD decoding, and, without Purevideo support that takes the load off the CPU when doing motion-adaptive deinterlacing, most CPU's would struggle to scale and deinterlace video for HD playback.
This is an excellent card for a non-multimedia (read: no videophile-level video playback and no gaming) computer, though. It's faster than any AGP-era onboard video (ATI Xpress 200M and nVidia 6100 and 6150 are faster, but they're PCI-E chipsets,) and DVI output enables much higher display quality to a DVI monitor than the badly-filtered blurry onboard video.