IMO your crazy. I feel you would be better off looking at Dell outlet web site and looking into getting an a older high end industry strength workstation with xeons processors with ECC RAM and a Photoshop supported GPU video card. You can always add SSd and more disk the disk controller will also support raid configurations.
Why build your own when you can get a pre built machine which meets your needs with legal OS and warrantee at a reasonable price.
I really hope you have Megabytes and Gigabytes confused there.
You need a couple Gig of RAM, and a Terabyte or more of disk space these days.
Out of curiosity, what's your budget?
I follow exactly JJMack's philosophy myself.
thanks chaps i got that wrong please read 500mb = 500gb .250mb =250gb .the ram should be 16gb exspandable to 32.gb. the buget is $2000 = £1200 . the op system is windows 7 pro .64 . i would like a multi card reader & b/w dvd and as many usbs as possible.some of my panos if i dont flatten them can be quite large and take 30min/50min .the present machine is 2core with 8gig ram ,500gb hd with500gb scratch disk on windos 7 64 home