Best OS version for Opteron cluster?

Well, hell may not have frozen over, but my purchase req for 5 dual-Opteron pizza boxes with 20GB of memory got approved, and now I have to figure out what to do with them.

I'm running a big FDTD electromagnetic simulation code I wrote myself, but at present it runs on Windows and OS/2, neither of which is terribly attractive on a 64-bit machine due to compiler issues, if nothing else. Accordingly I'm planning to use Linux, but you could fit my Linux expertise into a matchbox without taking the matches out first. Fortunately the code is all console mode, and I think I have the slight differences in the sockets API figured out--if not, it's not a big deal to fix.

What distro is best for this kind of service?  Any other experiences to share?

Cheers,

Phil Hobbs
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