Thanks to all the advice on this board, I have my htpc up and running with just a few kinks to iron out.

It's an Asus M2N VM HDMI motherboard (7050pv) with an Athlon 5600+ and a Pixelview B1000 hybrid analogue/dbv-t card. I'm running windows xp with sp3 and media portal installed as per the Cranz tutorial (minus the epg stuff), and the PowerDVD8 Codec.

My main issue is TV3.

If I use VMR9, I get around 10-30% cpu usage (depending on channel) and everything works fine, except TV3.  Everytime I switch to TV3 I get the audio with a distorted green blocky video, video freezes a couple of seconds later, then the sound stops and finally mediaportal freezes entirely.
If I switch to EVR (I've installed .NET3) I get all the channels including TV3, but CPU usage sits around the 40-60%, and I get occasional pixellation and the general quality isn't as good - video looks like it's running at a lower frame-rate.

I thought maybe the system couldn't cope with the demands of 1080i, but if 1080i works in EVR, which seems to require more processing power, I think it may be another issue or an option I need to change somewhere.

Any help would be appreciated.

As a side note, is it possible to turn of timeshifting? I don't think I'll ever use it, and it seems to chew up a little more resources for the first 30seconds or so after I change a channel, and is unnecessary.