Freeze on Windows 7 RC1 32 & 64 bit

I use deeply Windows 7 RC1 on 2 PC (12 h at day).
A) Intel 2x 2.80Ghz 32 bit 2 GB RAM 500 GB SATA ATI pcieex x1550
B) AMD Athlon 64 X2 64 bit 2GB RAM 1,3 TB SATA NVIDIA 8300 HDMI
On PC A) freezes are not frequently but 5 or 6 at day. The more times happens when I use mouse but not with specific program (on IE 8, on Skype 4, on Winamp) . Mouse is standard Microsoft PS2 mouse. Same mouse works perfectly with Vista 32 ultimate on same hardware and same programs. No indication on event log.
On PC B) freezes are each 15 minutes when I use for seeing a movie.
I tried with different programs (K-lite Codecs, KMPlayer ) with HD resolutions but with same problems. Same hardware, same movie , same programs with Vista Ultimate 64 bit Service Pack 2 works perfectly.