Caelinux cluster

Hi,
the best config depends on what code you will use.
For Aster, a fast hdd and a lot of ram is a must (8Gb is a good deal), something like a Phenom II X4 965 or Intel I5 750 (or higher like I7 860, 950 if you can) is a good choice.
For CFD, in most cases, you don't need such high memory (but 4Gb is a minimum), but a good network bandwidth and a lot of fast cpus. So something a good Core I7 or Phenom II X6 would be a good choice.
Personnally, as I don't earn money with my CAELinux activities (the DVD orders just pay my running costs and a few spare parts), I pay much attention to the performance per euros. For me the best deals are to buy parts and build a system myself. In that aspect AMD has the best offers and you can build a nice 4 cores Phenom II X4 965@3.4Ghz / 8Gb ram system for much less than 1000 euros today.

Or you can wait for CAELinux 2010 on Amazon EC2 and pay "per use".
With 1000 euros, you can run approximatelly 500 hours of computation on a 64Gb, 8 cpu machine (best for large Aster jobs) or 330 hours of computation on a 4 node cluster of 8 cores 2.5 Ghz Xeons ( thats a lot a cpus, 32!)
And you can get even lower prices if you use Spot instances.
see aws.amazon.com/ec2/ for more info.