I use a different codec though (ArcSoft total media theatre trial) and use DVB Viewer as I had issues with Media Portal RC1.
All channels display fine and with low cpu usage. Only issue is sometimes swtiching between channels I lose the picture but the sound continues. I would then just have to go forward and back again to get the picture.
Last week though Windows Vista downloaded an update and as soon as I launch dvb viewer it blue screens. Haven't had a chance to remove this yet.