how to build a MCE system.

[CrimandEvil]

ATI TV Wonder Elite PCI

All 550 based cards are made equal, ATI's just cost the most and has the most useless junk.

Dvico FusionHDTV3 Gold QAM

Fusion 5 Lite PCI HDtv tuner card

The Fusion 5 is the updated model.

which one is better?

Apples and oranges son, you're comparing an SD tuner to an HD tuner. Also since you're using MCE if you went with the HD tuner you'll still have to get an SD tuner for it to work. In MCE HD support is simply an add on because the core PVR app is centered around SD content still.

I have Directtv box right now.

Then you'll have to use svideo out to the tuner card, in that case get a 550 based card because it does better processing on analog inputted content then the PVR150.