AM2, X2, Opteron, or Opteron Socket F?

I recently gave my trusty, rock solid Athlon 64 X2 4400+ system to my wife 
(long story there, but it had to be done.) That leaves me with my 
not-so-trusty laptop and a searing desire to build a new system.

My problem is deciding on a processor and motherboard.

At first, I liked Intel Core 2 Duo, but the motherboard selection doesn't 
seem great and it is very pricy.

Then I looked at socket 939 procs...I love them...but they can't do DDR2 
memory.

I'm also confused by the advantages of Socket F, socket 940 (which I know 
allows DDR2 memory), and the advantages of Opterons over Athlon 64s or 
Athlon 64 X2. Or vice versa.

I need to do some heavy, heavy database programming and website building in 
the next 2 years. I want quick ethernet controllers. I'll be working mainly 
on a Linux platform, Fedora Core or possibly Red Hat Enterprise Linux.

What AMD processor and motherboard would work best for me? Should I focus on 
Opterons?

One last note -- my old system has an Asrock DualSATA-939 motherboard 
running the 2.20 BIOS. I took out the old ATI 9700 All-In-Wonder (AGP) video 
card and put a BFG GeForce 7600 GT OC in the PCI Express slot. It works 
great and powers my wife's 24" flat panel monitor at 1920 X 1200 resolution.


Thanks

Bob Cochran