What is your budget? What requirements do you have (SLI, RAID015, etc)? Will you be overclocking?
For most components, lower speed and lower voltage = less heat. For memory, that means get 1.8v DDR2 memory that is as slow as you need (current cpus only need 533 RAM at stock speed but forthcoming cpus later this year will need 667 RAM).
Antec Performance One series cases are quietish (very quiet if you replace the Tri-Cool fans). P180B is popular. P182 is an upgraded P180 with cable management but has Tri-Cool fan speed controls on the rear of the case (which means a small hole will be at the top back of the case if you switch out the fans).
Noctua NF-S12-1200 are very good very quiet fans. Noctua NH-U12F is a good (not quite as good as Tuniq Tower or Thermalright Ultra 120) and very quiet cpu cooler.
I think about the quietest PSU you can get is a Seasonic S12 Energy+. Only possible drawback is that it is not modular (if you want modular and quiet, look at the Corsair HX (actually made by Seasonic)).
Sounds like you want the fastest CPU which is the e6600, Good RAM with heat spreaders (longerlife), a passive cooled GPU and all the quiet stuff Wilcoxon suggested. Many motherboards have better cooling, mostly on the chipsets but Gigabyte have better Caps for longer life, depending on your need for Firewire I suggest the DS3/DS4.
Windows XP Pro is best all around OS, but if your programs support 64-bit, then get Pro64 and 4 GB of Ram.
I have 3 Antec Sonata IIs and they are very quiet and never had a heat problem. The PSU is sufficient for the AMD X2 4200. Using an ASUS 939 board with passive cooling so the system is very quiet. Obviously you don't want a 939 board. AMD seems to run cooler than Intel but for rendering Intel is faster. For video I set up a very inexpensive X2 3800 system that I use to capture, edit, and burn video because everything simply takes so long. It works fine and frees up my other machine. You may want to think about using your old machine just for the video and build the new one for everything else you do.
Thanks for all your suggestions, was busy checking everything out.
My budget is around $2000. I don't think I need 2 video cards, just one of the best there is. I also might stick to SCSI (Adaptec 29320 + Seagate Cheetah 147GB 15K RPM) since I have not seen a SATA system that is faster than my current one, besides that it frees up CPU usage, no intention to overclock. Does anybody know which MBs are compatible with SCSI?
I read somewhere on these forumz that the Xeon 3070 is a better choice for a quiet system (less heat). Any thoughts on that? What are the differences between this one and the E6700?
What online suppliers are you using that have competative prices? The company I used when I built my old system unfortunately closed down.
I do a lot of heavy multi tasking, are any MBs, GPUs etc. preferable for that? Other aspects to consider?
then the only reason to get a 64bit OS is the extra RAM. I am going to try it with some of new builds, but nothing I need to keep running. It is the future but problems equal added features, so proceed with caution, as in dual boot to start.