It might be an option to go with an Athlon 64 X2 instead of the Core 2 Duo. I'll explain why.
In 64-bit benchmarks comparing dual Opteron 285 CPUs (dual core 2.6 GHz, 2MB L2) against dual Xeon 5160 CPUs (dual core 3.0 GHz, 4MB L2), the Opterons are marginally faster in about half the tests. It's fairly even.
"Why does it matter then?" you might be asking.
Well, first realize that the Xeon 51x0 series processors are based on Core 2 Duo architecture, just like the desktop chips are. They perform almost identically. The only real differences are that the Xeons have more cache in some comparisons against the desktop chips and can run with more than one processor in a system.
Secondly, realize that the Opteron dual core chips and the Athlon 64 X2 chips are both based on 90nm K8 architecture. The Opterons are capable of having multiple processors like the Xeons are. The Opterons do not have more cache than the X2s.
The third point is the frequency difference. The Xeons were operating at 3.0 GHz and the Opterons were operating at 2.6 GHz. Since both of these architectures scale linearly (almost), it's safe to guess that a 2.6 GHz Xeon machine based on the Core 2 Duo architecture would have been slower on every account, up to about 15%.
So, if the AMD K8 dual core processors are faster than the Core 2 Duo processors at a given frequency with half the cache, what is the price difference? The AMD is actually about $30 cheaper.
Athlon 64 X2 4400+ (2MB L2, 2.20 GHz, Dual-Core, Socket 939)
$237.93
http://www.ewiz.com/detail.php?name=A64-44CDBXIntel Core 2 Duo E4400 (2MB L2, 2.13 GHz, Dual-Core, Socket T)
$264.71
http://www.ewiz.com/detail.php?name=E6400Remember that this argument is for 64-bit performance. Right now, that isn't terribly important as most people run 32-bit Windows XP and the 64-bit edition isn't really "ready" IMO. The Core 2 Duo processors are faster than the AMD hardware in 32-bit performance. They do
not appear to be as fast at 64-bit performance.
As of early 2007, 64-bit performance will become important to those people building for Windows Vista. So while XP might be slightly faster on Intel hardware now, Vista will be slightly faster on AMD hardware in four or five months.
This recommendation holds true so long as you do not intend to overclock. The Intel Core 2 Duo processors will overclock more than the AMD processors as a rule. Since you could get an E6400 to clock high enough to overcome an overclocked AMD processor, the price difference would also be negated. However, since you do not want to overclock your computer, these points I've presented should be rather interesting to you.