I've found an workaround
. I have just to change the resolution of the screen (via nvidia-settings) to another resolution and then back to the default resolution if I want to issue another suspend cycle. This makes the video card to re-initialize itself and then I can suspend without problems. I've tested with 9626 but I think that this shoud work with newer version of the driver as well.
I'm soooo happpyyy
While writting this post I have just resumed for the 17th time
Thanks nvidia people for the good work, now I have 3D acceleration,beryl and suspend all working on my old ti4200 card.
P.S. Is there a way to issue the resolution change from command line to put it in the hibernate script? Thanks, again. Now I let you concentrate to the black window bug with Beryl / Compiz