I use CCCP and manually register MPCvideodec.ax for DXVA playback (and disabled in CCCP). I also am using a unlocked sempron 140, but at 2.7GHz and CnQ enabled. I do not have a BDrom yet, but my 720P and 1080p files play back just fine on one monitor while I email and stuff on the other

Slight skipping in the file if I am running a flash app.
The ATI drivers include VC1 acceleration I believe (BDrom ) so you just need WMP/WMC to play them back.
Oh... in windows 7 disable MPEG2 playback in CCCP also. Windows7 codec works just fine and replacing it with the inferior ffdshow codec is not advisable and can cause MC to crash.