Choppy video on Zotac Zbox AD04

Hello everybody.

I have bought a Zotac Zbox AD04 (AMD Fusion), installed with 32-bit Windows 7. I have installed the latest Catalyst-driver and the latest XBMC.

But I have trouble with playing "most" video. AVI-files mostly work, but DVD-rips in ISO/IMG are really choppy and just doesn' work.

I haven't changed any settings beside setting audio to HDMI. dxva2 was enabled already.. I have tried different options (disabling areo, using fullscreen window) but so far no luck.

Can anybody point me in the right direction on what to do?

Thanks,
Audun