We are thinking about putting together a cluster of maybe 10 machines, 
presumably using GNU/Linux.  Do any of you have experience with this?

Some of the things I'm wondering about include the appropriate 
configuration of machines -- isn't it better in terms of cost/benefit to 
buy fewer dual quad-core machines than more single CPU machines, 
especially if the jobs are not very memory-instensive?

We certainly want to use shared disks, but is there any problem with 
booting all the computers from the same network drive?  That seems like a 
good idea to me rather than to have separate HDDs in the machines, but I'm 
not sure how it is done.

What free software is available for managing jobs, e.g., batch queuing?

FYI ... The idea is to use these machines for our genetic analyses -- 
maybe 600,000 SNPs on 7,500 people, but this mostly consists of running 
one SNP at a time on some collection of traits.  I don't think the memory 
requirements are too great unless we try to load a lot of the data at 
once.

Mike