The Prolink card is a dumb terminal, of sorts. Without an integrated graphics chipset generating an SDVO signal it's useless. It's essentially a video passthrough as well as an audio passthrough (with the HD Audio link header) and the northbridge (graphics) and southbridge (sound) do all the heavy lifting.
It's not a popular solution as up to now it's been incapable of the most useful HDMI task: HD DVD/Blu-ray disks. We'll see if that changes, now. I think the availability of 7.1 LPCM could give it some market advantage in the HTPC niche, but as I mentioned it remains to be seen if that passes muster in terms of content protection in PowerDVD. If it doesn't have that, it has very little advantage over, say, an Nvidia 8600 passively cooled card.
Actually, the G33 and G35 should support it as well-- if not in this release, in one coming soon. The patch which enables it in PowerDVD mentions the older 945G chipset, too... but that seems a bit far-fetched to me and might be a typo. Would be impressive if it worked, though-- there are a lot of 945G machines out there.
I do not speak officially in any sense for
Intel Corp., Technology Manufacturing Group
but I do work there.