with dell as with probably most other brand you'll have to deal with high prices for their nonstandard replacement parts. proprietary mobo's, power supply's, etc. but i can understand that you shy away from building a work machine yourself. i'll go that route too for my next box which will not be supposed to run games…
Ram: Avoid the fancy DDR433 or greater frequencies, they are made for overclockers and not the 'normal' user as most boards only take upto DDR400. As we all know overclocking makes the machine unstable. Also be sure you buy dual channel matched pair 2x1gb's and the timing is 2-2-2...I recommend Kingston, Corsair or Patriot…