I built an extra PC just to use as a PVR using an ATI All-in-Wonder 9000 card. It can record from the tuner to either MPEG-2, MPEG-1, Windows Media or the ATI VCR codec. Strange thing is when I have it record to .MPG or .WMV, the resulting file will play fine on the machine that recorded it. But when I try to view these files on another computer, it says 'Failed to Render file'.
When recording to the native ATI VCR format, it creates files of .VCR extension, which obviously cant be dealt with natively on another PC. But files recorded to this format yield an extra 'Export to MPEG-2' option when right-clicked in the native ATI application. Strangely the resulting .MPG files from that opeation will play on other machines.
Followup: OK the issue seems to be more with Windows File Sharing in some way, rather than with codecs. I find that if I record a clip on the machine with the ATI card in it, the networked machine wont be able to see them. BUt then if I unshare the directory on the ATI machine and then activate sharing again, then the networked machine can open it.