My plans are to switch the psu fan to a panaflo & use a thermalright sk7 w/ 80mm panaflo (w/ zalman fanmate) & and then use rubber isolators to mount the case fans, use a zalman heat sink on the northbridge chipset and lastly the zalman heat pipe on the vga card. - After all this, I would only have 80mm low to medium speed fans (no more high speed northbridge / vga or cpu fans)
You can beat a Dell. Their low noise system specs are based on the quietest config for the particular series, so...
A key question to ask is whether the in/out case air vents are free and open. If not, consider a new case or some cutting work. This makes a big difference, because an unrestricted airflow path is the #1 key to making low speed quiet fans cool effectively.
You can forego the vga heatpipe cooler. You might do fine with just a VGA-fan bracket from Zalman -- with a Panaflo. Just disconnect or remove the orig fan on the VGA & run a Panaflo on the bracket at ~5-7V. Saves you lots of $ and hassles (that heatpipe cooler is a pain to install). Also the Zalman ZM17 works well even on GF4 ti4600 in combo with the fan bracket cooling. (or a homemade variant -- see my P4 system quieting article
for a DIY version using a PCI slot cover)
The PSU fan swap will probably get you some improvement, but if the fan is running at 12V all the time, or runs off a dumb thermistor control, it will still not be that quiet. Probably >30 dBA in the PSU with all the turbulence & vibration, even with a Panaflo L. I suggest you invest in some Zalman fanmate1 fan controllers and/or a Zalman multi-controller. You can run the new PSU fan leads out of the PSU and feed it off a controller to adjust the voltage. Don't forget to ensure good airflow through the PSU by cutting away any unnecessary fan grill, and doing the 90 degree pivot on the intake vent side. (see Leo's Dual-MP system article
Finally, you will want to at least put your IBM drive on a sheet of soft foam on the bottom of your case. Once the other work has been done, this simple move will make such an enormous difference you will shake your head in amazement.
Have fun & good luck!