Vista Freezing problems with nvidia chipset based mbd

Hi guys and gals,

I have just built a media center PC for myself and am having weird 'freezes' - I have also seen this in other PCs that I have installed with nVidia chipsets/AMD CPUs.

Basically what happens is the PC runs fine then at seemingly random points, it appears to 'freeze' where I can move the mouse around and even bring the Start menu up but nothing else. The hard drive activity light goes solid and nothing responds for between 30 seconds and 2 minutes (I haven't timed it exactly), then all of a sudden, it comes back to life and carries on fine, until a few minutes later, it does it again, ad infinitum. This is a fresh install of Vista Ultimate with the very latest nVidia chipset drivers and graphics card drivers. There isn't a BIOS update available. Like I said above, I have seen this before with nvidia chipsets on other people's PCs.

My specs:

AMD Athlon64 4000 Socket 939
ASRock 939N68PV-GLAN motherboard with a nVidia nforce 630a chipset with the latest 14.10 drivers
ATi Radeon HD2400 graphics card with 8.3 drivers
Samsung Spinpoint 250GB SATA HDD

I don't think you need to know any other details, but I can provide them if you want.

Any input/help would be appreciated as this problem renders the Media Center side of things un-usable as the TV keeps 'freezing'