Without any more info to go on, freezes like that, in my experience, are most often bad RAM or a bad video card/driver. Do get a bluescreen?? Or does it just freeze.
You can test the memory with memtest86:
http://www.memtest86.com/
It will create a bootable floppy for ya. You shouldn't see any errors.
Or load up the Vaio support page at
http://ciscdb.sel.sony.com/perl/select-p-n.pl
and hit the auto-detect option, see if there's any hardware diagnostics you can download. They could very well have updated drivers too.
Is the laptop new? See if it's still under warranty and have it RMA'ed if so!