I'm looking to build a new computer at around $500-$700
It will be used mainly for design studies assignments: Adobe Photoshop, Illustartor, In-Design, Premiere and After-Effects CS4/CS5, and also home usage (MS office, video, music etc.)
It will be running win7 64bit.
I understand CUDA support can improve performance in CS4/CS5 and I'd like to use that.
Looks like you actually did a pretty good job of selecting fairly decent stuff. If this fits your budget, I would recommend you proceed. Others will tweak your build, but that process can drag on endlessly with someone always having a better idea or deal for you. You did good. Move out. HOOAH!!!
I would check to see if the software you plan to use can take advantage of a six-core CPU. I would say it's unlikely. You could save some money with a quad-core and a better graphics card and get better performance. Again, a lot depends on what your software can take advantage of.
For instance, maybe take your original build and go with the Zotac GT 240 for a few dollars more?