If you are going to be using this computer mainly for SolidWorks you will need to get either an nvidia geforce FX card or the ATI fireGL card to properly run SolidWorks features. . Both of these cards have passed the Solidworks tests and are recommended by SolidWorks. Any geforce or Radeon card have not passed the tests and are not recommended. I would also get at least 4 gig of memory. Every thing else looks good
Simulation (Cosmos),photoworks and photoview 360 will take advantage of the multiple cores. Besides that SolidWorks mainly uses a single core. That being said, I would agree with cjl and go with a guad core.
Video Card: I am a little paranoid when it comes to the video card. If I get a SolidWorks approved card I will end of paying $300 more than I have to spend. I found an article (I cant find it now) that benchmarked the GeForce 9800 GTX+ against workstation cards and it performed very well in all tests except the synthetic test. I am afraid using any other card unless I can find evidence that it will work well. I know that video card problems can inflict much misery so I am try to be cautious without spending $500 on a card. Probably the reason the one that is listed is overpriced because is comes with a game.
As you can see, none of the nvidia geforce cards are recommended and the system build says you need an OpenGL card (quadroFX). The main reason why you need a guadro FX card is manily because it uses OpenGL which is what SolidWorks (as well as most CAD programs) uses. Video games use DirectX10 which is what the geforce cards use. This card may work for simple parts/assemblies/drawings, but when you get to complex parts or large assemblies/drawings, you will see a large difference between the gefoce and guadroFX cards. If there is one component that you should splurge on it is getting a nvidia guadroFX graphics card.
In my line of business I have talked to hundreds of people that have had issues with SolidWorks that are caused by them not using a recommended card. If you have access to the SolidWorks customer portal I would recommend going to the knowledge base (found under "my support") and do a search for "geforce". You will find many issues that are cause by these cards. Hopefully this is enough information to help you see why I stress so much on getting a recommended QuadroFX card.
I should have linked my guide, which will clarify the RAM issue a bit. Since you are on a tight budget, 800Mhz RAM will work fine. You would not see any real gains from faster RAM unless you are overclocking beyond 400FSB.
From the SolidWorks site, it looks to me that specific hardware is not so much the issue. The issue is that it needs the workstation card DRIVERS to run well... this is similar to many other professional programs.
If Chadley says you need a Quaddro, perhaps you'll need to rethink some of the other parts to make room for it.