I've had the exact same thing happen to me, and I haven't figured it out yet. My computer ran great for the first month, but it's been freezing much more often lately. List what your computer specs are, and we'll compare them.
Mine is configured as follows:
Asus Striker II Extreme motheroard with the Nvidia 790i chip set.
2 1-gig Palit 8800GT graphic cards running in SLI
Intel Quad Core 9450 (not overclocked)
Asetek Liqid cooler
2 500-gig Western Digital hard drives (7200rpm) in RAID
4-gig Corsair DDR3 1333 Memory
Windows Vista Ultimate (64bit)
I haven't yet tried a Bios update for the Striker II motherboard, but I've got a feeling that might work.
Also, I've heard of compatability problems with 64-bit Vista and the 8800GT cards.
If it freezes on audio, then your sound card or drivers are suspect. Update the drivers and see if it helps.
There are no compatibility issues with 8800GT cards and 64-bit Vista. I know, because that's precisely what I'm running. There might be some issues with SLI that I don't know about because I'm not running an SLI config.
To the last poster, you might want to consider making sure all of your RAM is installed in matched pairs... especially if you're running in dual-channel mode. It wouldn't hurt to update your BIOS either.