Is it enough?

Do you think that a 350W PSU with 15A on the +12V rail be enough for the following, possible spec of a render farm slave, no DVD or hard drive:

AMD Athlon 64 X2 4600+ 2.4GHz AM2 1MB
Asus M2N-E, nForce 570
Corsair TWIN2X 5400 DDR2, 1024MB PC5400 Kit
POINT OF VIEW GeForce 7300GS 256MB DDR Turbo Cache

I have my doubts so does anyone know if the PSU in the Coolermaster Cavalier 4 can be upgraded? Is it a standard ATX PSU?

I think your doubts are well founded. Most cases that come with a predetermined PSU don't offer an upgrade.

If it is a good quality PSU, that would suffice. With a PSU that came with the case a la Aspire...I would not use that.

I plugged your components in here as best I could:
http://extreme.outervision.com/PSUEngine

The calculator said you needed 178W, so that 350W psu should be good enough imho. Now it really depends on the quality of the PSU, and I'm not sure who makes the CM ones (perhaps OklahomaWolf or SuperNade can chime in here).

It is a bit disconcerting that there is only 180W available on the 12V line, but honestly, your system would only use 178W TOTAL at peak, so I don't really see an issue, unless the PSU requires high crossloading of the other rails to achieve good 12V performance.

My suggestion to you is to go ahead and try it, and measure the 12V line at peak with a multimeter (as shown in the sticky). If it doesn't like it, then get a new PSU. The 400W Enhance is a definite winner, but might be overkill, a 400W Forton or Sparkle or XClio 450W are also great choices (for around 40-50 shipped).

I can pretty much guarantee that the Cavalier comes with a standard ATX psu.

Thanks for that. I was just wondering what other cases of that style would be recommended that would be nice and cheap without PSU. I am considering this style as they could easily be stacked for the render farm, if they want it

Sorry, it seems I was wrong about the PSU, it is indeed a proprietary size.

http://www.pcper.com/article.php?aid=104&type=expert&pid=6

As for the machine itself, have you considered something like this:
http://www.newegg.com/Product/Product.asp?Item=N82E16856101011

Small, stackable, and affordable when you consider that mobo, case, psu, gpu, and cooling is taken care of. In your situation all your really need to add there is ram and processor.