Well
generally MOBO's don't use much power themselves, but going by the minimum of
one component doesn't seem like a solid call for me...
But, as Mika said, stable power from all lines is usually more important than having a lot of power surplus in general. In short - get a PSU that can continuously product your system's peak power consumption on all lines.
As far as component wattages go, I'd leave that 350W margin for the GPU alone, then 70 or 90W for the CPU (Venice Athlon64 max power is 67W IIRC, San Diegos can eat up to 89W) and then some for the other stuff and peripherals. 430-450 W in simple add-up calculation; depending on your USB and FireWire device power consumption, 500W might not hurt either.
Then again, I have very similar system (MSI MS-7184 Socket939 motherboard, Athlon64 3200+ (venice), 3 GB dual channel DDR, one 200GB SATA HD, one 320GB E-IDE HD, GeForce 7600GT) and I haven't had any random restarts even though I "only" have a 400W true power PSU. It's this one:
Nexus NX-4096. I don't have as many peripherals connectd, though...
But, as was already said, it's more important to have guaranteed continuous power than loads of surplus wattage (which won't be used anyway). The problem is, many cheapo PSU manufacturers don't announce the continuous power output but instead some rounded number between continuous and peak output power. Other problem is voltage fluctuations which can make the PC shutdown or even destroy components... It's the other thing you should be interested in isntead of surplus wattage. Is your PSU of any known quality brand?
My advice is the same as Mika's - go for quality. Count the component peak wattage together, add some surplus but not too much (no use in paying for 100 or 200 extra watts of power that is never used eh?) and then get a PSU that really produces that power continuously and with minimum voltage fluctuations. I can only say I've been extremely happy with my Nexus PSU, since it not only keeps my system stable and running, it's also extremely quiet.
And pay attention to the amperes on the voltage rails as well... PArticularly the 12V and +-5V rails. I don't remember the recommended numbers but there are a lot of sites that have good instructions on them...
By the way, my MOBO (or rather, BIOS) can't really do anything to clocks either but I found a nice application called ClockGen that can be used to boost the FSB clocks via XP... so I now have the FSB set to 220 MHz, and subsequently the processor clock went to 2200 MHz due to tenfold multiplyer. What's nice is that it also boosts PCI and PCI-e frequency and thus their memory bandwidth. It's only 10% increase but what the hell...
You might also want to check if your 7600GT can be clocked to any degree. I don't know if there's any overclocking utilities in NVidia's Linux drivers though... but just for the record, my card runs stable and cool clocked to 720/1750 MHz for core/memory, but I usualyl prefer to run it at it's factory clocks (650/1600 MHz) because at least on my system, the CPU starts to form a bottleneck anyway before the GPU.
