The Dual Core Intel's would be your best option here they are more robust than the AMD ones and from my experience far more reliable for a Server Application.
As for performance I have a Dual Xeon 3.2 unit here and I'm running it beside a Dual Core Pentium Extreme which is a Dual Core with HTT and 3.2 speed so in theory it should be faster than the Xeon but for all piratical purposes the Xeon beats it hands down every time. But with only 15 users this might not be much of an issue for you unless there is a lot of network traffic involved where a lot of number crunching needs to be done on the server.
What I can not tell you however is what will happen if one of the cores fails as that is something that I have not as yet seen. With a Dual Processor you can always run it with one CPU while the replacement is found but I don't know what will be the position if one of these Dual Core CPU's breaks down. It could take the server Off Line totally or just slow it down dramatically.
If this was a [b]Mission Critical Server[/b] I would stick with the Dual Processor configuration as they have a known past to work from where as the Dual Core CPU's are as yet not on the market long enough to fully understand what will happen if something goes wrong.
But that's just my opinion you know better how important your Work place is and what the loadings will be. It's just that with a Dual CPU Setup it's possible to overheat one of the CPU's without damaging the other in theory where as with the Dual Core with everything on the same chip it's anyones guess as to what will happen.
Col
