Considering your uses I would suggest you wait until January 9th, when Intel release their next generation "Sandy Bridge" CPUs.
These chips will be
faster for CPU heavy apps like photoshop than current generation CPUs and even the quad cores are only 95W TDP (and use the 32nm process) - so running them cool and quiet won't be too tough.
Sounds like very sound advice to me.
Another possible advantage to SB is that they will have graphics cores built into the chip, so unless you want to utilize CUDA, which I think is unnecessary, then you won't need to buy a graphics card and worry about keeping it quiet or cool enough.
Other components choices can still be discussed today however, such as case, PSU, fans etc.
For a quiet PSU I personally would go for one from the Nexus RX Real Silent range, as they are high quality, have decent efficiency, 80Plus Bronze, are below £100 in price and are probably the quietest fan cooled PSUs around. The Nexus Value-430 is the cheapest one and is also very quiet, altho only have 80Plus efficiency
Altho it sounds like you'd be more interested in a fanless or sem-fanless PSU. In which case you'd probably have to go for a Seasonic X-400, or one of the others if it's cheaper, as if you build a system with a low enough power draw it would almost never cause the fan to spin in, say, the X-650 or X-560. These cost more than £100, but have the advantage of being much more efficient, 80Plus Gold, and are all modular (some of the Nexus ones aren't).
Reading SPCR should give you some good ideas for a case, fans and heatsink.
http://www.silentpcreview.com/Recommended_Heatsinks
http://www.silentpcreview.com/article75-page5.html
http://www.silentpcreview.com/article63-page2.html
You'll probably be looking at an SSD for your OS and programs, while putting any higher capacity mechanical drives (probably green ones - WD Caviar Green or Samsung Spinpoint Eco Green) in a HDD silencer.
