How much can a 350watt power supply handle?

I have e a computer that has an AMD Opteron170 with 2gigs of ram, a GeForce 7900GS with 256megs, an Audigy2ZS sound card, and two DVD burners, a SATA WD 74gig Raptor, and an EIDE WD 160 gig HD. The motherboard is an ASUS A8Ne. I'm thinking of putting a second EIDE drive as a slave and unplug the power to the second DVD drive. My operating system is on the RAPTOR, but there is enough software on the first EIDE that I really don't want to unplug it. My reason for installing a second EIDE(a 120gig) is to install Windows Vista on it and be able to uninstall it in case it goes awry. Both the 160 gig and 120 gig are from a previous system, and both have the same WinXP on it, and are essentially identical, because I "ghosted" the contents of the 120 onto the 160, and since then, the 160 has a few programs as well as more MP3s added to it.
The CPU is cooled by a Zalman fan, the Video card has a stock cooling fan, and there is a 4" case fan as well. My question: considering that my computer has been running fine for 3 or 4 months now, is it a reasonable tradeoff to reduce the power consumption by one DVD burner and add the demand of a 120 gig HD? Is the HD power demand equivalent to that of a DVD drive, or is it a much greater power hog? I don't know the make of the power supply, but it was advertised as a high quality one. I bought the computer used, and judging from the quality of the other components,
I believe that it is a capable one.
A second question: It is reasonable to install VISTA on a secondary(slave) EIDE and select it as a boot drive in the POST sequence, isn't it? The readme file on the Vista disk speaks of being able to install the OS on a separate partition, but never mentions a separate drive. Is it just semantics?
Thanks.

 

There's really no way that anyone can answer specific questions about your your specific setup. PSU capabilities vary wildly even if they have the same wattage rating.

My feeling is that you're "pushing it" with a 350W PSU but for all I know you might be able to run your rig for years with that PSU with no trouble.

I've never used the calculator that Pete mentioned but have relied more on my own experiences and intuition I guess. A mediocre quality PSU can throw a real wrench into that calculator's "equation ".

The best way to rid yourself of PSU problems or even questions about whether your system may soon give you problems is to stay a bit "ahead of the curve" by buying more power than you actually need and sticking to very high-quality brands. About two years ago, I bought a quality 550W PSU and haven't had a "power problem" since even through several upgrades.

The more I learn of PSUs, the more money I end up spending on high-end brands/models. They really are a critical component of any system.

 

Thanks for your replies. I made this a potential problem purely out of ignorance, but more out of the short memory that accompanies someone my age. I took the power supply out of the case, and it turns out to be a 435watt unit. The -12V rail is rated for 14amps, and the -12V2 is 15.
I frankly don't know what all that means, just repeating what I read here and there.
Using the calculator that PeteC pointed me to, I come up with a demand of approximately 375watts, driving 3 harddrives. Over the years, I've been inside and built from scratch a good number of computers. I started out in the 486DX66 days by buying a case with a power supply for $28, and several years later bought an Enermax 350 watt on ebay for $55. This one came with the computer I purchased, and it looks to be a quality PS.
I think I'll be ok.
Thanks again.