I just got my 3450 from Newegg and popped it into one of my HTPCs. This particular HTPC had problems playing VC-1 content from HD-DVDs. The video stream is not re-encoded and it is muxed into a WMV container. The audio stream is re-encoded to WMA 5.1. My previous video card in the system was a Geforce 6800 AGP (this is a Asrock 939 mobo with AGP and PCI-E). The CPU is a AMD X2 3800.
The drivers that came with the CD are version 7.11, but I downloaded and used the 8.1 drivers from AMD's site instead. The packaging included a DVI to VGA adapter and a component video dongle. It did not include the special DVI to HDMI adapter that allows for HDMI audio. I did have a spare ATI adapter lying around and the HDMI audio does work on this card.
As far as the VC-1 content, playback has improved. However, I still noted high CPU usage (nearing 100%). I'm using the default Windows WMVVideo Decoder DMO to decode and I am on Windows XP MCE 2005. But, like I said, there was a noticeable difference with only minor skipping. The previous video card caused these videos to not be watchable.
I was still curious about the high CPU usage and the minor skipping. I couldn't find the checkboxes to enable wmv acceleartion so I wasn't sure if this was actually working. So, I just tried overclocking my processor a bit from 2.0ghz to 2.15 ghz and now playback is smooth. CPU usage on this high bitrate VC-1 content is now at around 70% for me. So, it still looks like you need some CPU power to playback this content.
As far as high bitrate h.264 is concerned, I didn't have a problem with this stuff with the old vid card. I also rip the h.264 elementary stream from HD-DVDs and just mux it into a new container (MKV for h.264 files). I do not re-encode them. Those have always played fine using the CoreAVC decoder for me and they still play fine with the new vid card.
I'll try 1080i mpeg2 content later tonight. And, if I'm not too tired, I'll pop it into my Vista machine that currently has a HD 2400 and is sucking big time at 1080i content!