Well I built a machine using an X2-3800 a while back
for my GF who now uses CS-2
the machine has 2 gigs of RAM and works great.
The machine is setup to dual boot XP 32 bit and XP 64 bit and since
Photoshop runs a little better
on the 64 bit side, she never bother with XP 32 bit any more.
Since the CPU you plan to get is so much faster than the 3800 here...
I think you will be pleased with the results.
I am sure 2 gigs of RAM will be fine and you may not notice that much differ
ence if you add more.
One the brief tests I ran, the fast , dual core CPU seemed to be more
important than the RAM.
When she was using a single core CPU some of the large images would take at
least a full minute to save.
When the dual core cpu was employed, the time was cut down to about 7
seconds.
Well worth it!