You could always upgrade then with the cversion.ini edit.Nope? Interesting. Maybe tell us which media player you use. WMP and VLC player and streaming HD video to PS3 is fine here.
PS: Seems it memory. I run the Beta still no problems and use 4 GB memory.
I want to upgrade to Win7 RC! but it needs a complete reinstall and I am not prepared to loose any data now. So it will have to wait a while.