Enermax makes very fine cases, dunno which one your looking at (and I'm not really going to look it up) but I think it is the steel one with rails and blue buttons and such. I think its on the small side, but thats just me I like very large cases for cooling and such. PSU is top rate, and 300w should be sufficent, contrary to everyone wanting 400w+ psus I'n most case it is purely excessive. If you were to actually add up all your wattage I think that even most gamming systems run in the 250's wattage range. Of course you need more than your using but still. In most cases PSU problems is an undervolt issue not wattage, and Enermax makes top notch PSUs so you should be good.
Also another suggestion I think you should run say just a 256 stick for now, I know most power users run 1/2 gig now, but DDR prices are on the rise and if you wait till spring you can save some cash. You know most memory manufcatuers are in debt (or recently out of debt) with the whole memory price fall a while back. So to make some extra cash they are reducing production artificially increasing prices. After the Christmas season they will drop again.
To the whole video card scene. Well as we all know Radeon 9700 is king and looks like Nvidia won't have any real competition at least this year. With NV28 comming out very soon (BTW NV28 is basically a GF4 Ti4600 + type thing based on the same basic core just faster), a Ti4600 may not be too unreasonable to purchase once that happens (as prices are surely to drop even further). NV30 will be something to watch out for but I don't think it will fit your timeframe. And if your looking for rather upper performance ATI has a huge hole, Radeon 8500 and then the Radeon 9700 no middleground in there (which might change but I doubt this year).
As to the 2.0A cpu your choice gives you more clock. BTW my terms of OC is rather basic I know lots of ppl will push fsb to 150s range and what not, but I am just suggesting 100 to 133 because it is easy and wont stress out your components so much.
18 x 133 = 2400
20 x 133 = 2660
Personal choice is 266mhz worth $20? (funny I never though I would ever say that considering it was a huge thing when the classic pentium series you could pay $100 more for +33mhz and it was a huge deal

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