I tend to think of OCing in increments of 66MHz. So in your case a Q6600 with an FSB of 333MHz (advertised as 1333MHz) should not be a problem. I'd get DDR2-800 memory even though your system may actually run just as well at DDR2-667 (also 333MHz). Intel boards like 1:1 FSBs.
Any board that has native 1333MHz support should handle your CPU fine, though I would recommend you at least read the user comments on NewEgg and once you decide on a board, the motherboard comments for that model both on NewEgg and Rebel's Haven Forum. Specifically you want to see for yourself how far others have successfully taking the cpu/board pair, although a great many leave the voltage part out. The BSEL mod would allow your board to boot up as native 333MHz FSB. Unlike OCing, everything should work perfectly, and trust me when you OC certain things just don't work, though they are not serious.
Any Intel P35 board should be OK, but this has a little more ooomph.
http://www.newegg.com/Product/Product.a ... 6813138075
There are alternatives.
I think this is a good lower profile cooler that would hold you for a while.
http://www.thermalright.com/new_a_page/ ... VzaWFzdA==
Its 63mm tall, way lower than a mini ninja. About 90mm tall with a fan. A Yate Loon 120mm fan on top and you'll be blowing air onto the board which is always a good thing. You need to measure to see if it fits, I have my fingers crossed for you.
With this cooler setup you may even keep the northbridge at a decent temp.
Your case seems to have 2 fan holes, hopefully 80mm on one side. The PS should probably suck in air from the side opposite the side that faces the back of the case. That suggests your Antec is better suited for the job from an airflow standpoint, but your Seasonic is most likely better built. I'm guessing it's 120mm would point up, which should work for it.
Obviously you should start at stock speeds, run Prime 95 (times 4!) and see what your temps in the case are. Prime95 times 4 will put the most stress on your system, more than folding.
If you think you would upgrade in the near future then I would ask why not start with an E8400? The 45nm dual will make far less heat, save you a few dollars, and maybe another $60 since the stock HS may work fine. You would OC from 3GHz to 3.6GHz no problem at all.
Are you planning on folding? You don't seem concerned with video at all, so you can get the cheapest card going, even an old used PCI card for like $10 should work OK. OCing and integrated video don't seem to go together on the Intel side, plenty to choose from the AMD side only.
And again the low requirements for video suggest you won't be buring DVDs or processing RAW photo files that are like 50-200MB each. 2Gig of memory is fine, DDR2-800 and no reason not to buy CAS4, the price differential is just way too small right now. Corsair or Crucial, about $35 for 2 1Gig sticks.