Don't panic yet.....take it one step at a time, and it's part of DIY.....one way or another, you'll get it working.....
1. Update the latest AMD driver from here- A8-3850
2. To get the best video/audio quality, you can connect your system this way- HTPC-->AVR-->HDTV via 2 HDMI cables. If there is an option in AVR, set it to pass-through video
3. Download the latest stable Eden 11.0
.....if you want to enjoy bitstreaming HD audio, you can download XBMC-RC2 HDAudio.zip
4. Select AMD HD HDMI audio output in Windows 7 control panel and XBMC settings/system/audio output (select WASAPI: AMD HDMI HD......)
5. Select DXVA as render method and enable DXVA2 in XBMC settings/video/playback, but disable everything else in it
6. Disable "Use a fullscreen window rather than a true fullscreen" in XBMC settings/system/video output
It should be a good start.....