MOBO:
ASUS P5E3 PREMIUM/WIFI-AP @n LGA 775 DDR3 Intel X48 ATX Intel Motherboard - $370
 
CPU:
Intel Core 2 Quad Q9300 Yorkfield 2.5GHz LGA 775 95W Quad-Core Processor 1333MHz FSB Model BX80580Q9300 - $285
----OR----
Intel Core 2 Quad Q6700 Kentsfield 2.66GHz LGA 775 95W Quad-Core Processor Model BX80562Q6700 -$275
----OR----
Intel Xeon X3360 Yorkfield 2.83GHz LGA 775 95W Quad-Core Processor Model BX80569X3360 - $565
 
RAM:
OCZ Platinum 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) - $421
----OR----
? Must be 1600 or above...  
 
GPU:
EVGA 512-P3-N845-AR GeForce 8800GTS (G92) KO 512MB 256-bit GDDR3 PCI Express 2.0 x16 - $255
----OR----
EVGA 512-P3-N877-AR GeForce 9800 GTX SSC 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP - $350
 
PSU:
ZALMAN ZM750-HP ATX12V V2.2 / EPS12V 750W Modular LED Heatpipe-Cooled SLI Power Supply - $190
----OR----
SeaSonic M12 SS-700HM ATX12V / EPS12V 700W Power Supply - $180
 
CPU COOLER:
ZALMAN CNPS 9700 NT 110mm 2 Ball Ultra Quiet CPU Cooler - $66
 
DRIVES:
System: Western Digital Raptor WD740ADFD 74GB 10,000 RPM SATA 1.5Gb/s Hard Drive - $140
Data: 2 x  Western Digital Caviar SE16 WD5000AAKS 500GB 7200 RPM SATA 3.0Gb/s Hard Drive (RAID 1) - $90
DVD:  ASUS 20X DVD±R DVD Burner with LightScribe Black SATA Model DRW-2014L1T - $35
 
CASE:
Antec P182 Gun Metal Black 0.8mm cold rolled steel ATX Mid Tower Computer Case - $170
 
OS:
Windows XP 64-bit (to be able to use all 4gb of RAM)
 
 
NOTES:
 
I am trying to stay somewhat quiet and also keep the budget under $3k USD.  
 
Has anyone had issues with Windows XP 64?  
 
Also, I am not really a big Vista fan - is DX 10 worth it?
 
Can anyone recommend some quiet PWM case fans?  I will probably put 3-4 in the case.
 
What kind of Wattage do you recommend for the power supply?

By workstation what do you mean, what kind of work will you be doing on it?

12-15 hours per day of running the following apps  (many of them simultaneously)  covering all aspects of web development, video editing and encoding, and a few hours of gaming per month.
 
Photoshop cs3
Dreamweaver cs3
Sony Vegas
Sorenson Squeeze
Firefox and IE
FTP Explorer

I say drop the DDR3 and go with DDR2. Overall, DDR3 doesn't offer that huge of an advantage, and you can easily get 8GB of DDR2 for $200.

runswindow s95, I really like that MOBO and it only supports DDR3.  Additionally, how can u say that DDR3 1600 does not offer a huge advantage over DDR2 800?  It is essentially twice as fast, no?

DDR3 currently has higher latencies than DDR2 memory (well since I last checked anyway), this will improve in time but for now most DDR3 memory is slower latency wise. Intel's FSB is also too small to realy take advantage of this ectra badwidth (however it still helps). In this case an increase in RAM would help many of your applications better than the increase is bandwidth you mostly cannot use.

Ok, answer me this....
 
If I have a quad core 2.86GHz at 1333Mhz and DDR3 1333Mhz then it will be running 1:1?  Without any overclock, won't that be faster than the same 2.86 or 2.66 running on DDR2 800?