Well, I am talking to someone about buying a GTX 460 1gb card (used, of course) or buying a GT210 or GT540 so I'm just comparing cards right now and assessing finances.
I read that's it's a PITA to try ATI cards with VDPAU.
Well, from the cards you're mentioning, I wouldn't recommend the GT210. It's old and its performance sometimes is even lower than current intel HD3000 IGPs. The used GTX460 seems a very attractive offer, if the card is in good conditions, and the best option of the 3 you mentioned. The GT540 is a great card for HTPC / light gaming.
I think you should give a look at Tom's Hardware VGA Charts...
There is a package in AUR "mesa-r600g-git" with vdpau enabled.
I have also installed:
You will need to export:
It's been working well for me for some months, but I don't watch a great deal of videos anyway.
To DanL and Execute_Method: Thanks for your help... after installing mesa-r600g-git + xf86-video-ati-git from AUR and creating a script on /etc/profile.d I was able to use vdpau on my HD4650 AGP card. Furthermore, this is the first time my card also works with dynpm ... As such, I'll stick to the FOSS drivers. It's unfortunate that vdpau on r600g still doesn't support H.264, so I can't watch 1080p H.264 videos on my P4 desktop (720p works well btw) ... I think that should've been a top priority in FOSS radeon driver development...