Virtual Machines and CentOS 5.0 [Linux]

[Scott R. Ehrlich]

Hello to all:

I have a a few PE2950III servers I'll be building up in the near future 
with 64-bit CentOS 5.0.

What performance experiences have list members had with running virtual 
machines (VMWare Server, VMWare ESX, etc) versus running applications 
directly in the host OS?

What are your experience differences between Xen and VMWare?

What is the real difference between the free VMWAre Server and VMware 
VSX[i]?   How about performance differences between these two products?

I want to try and plan correctly ahead of time, and real-world experience 
counts for everything here.

I really don't know what people will be doing, but I've seen people tax 
the machines with their code, though no machine has ever needed to be 
rebooted from being hung, nor has access to a system been blocked due to 
lack of physical resources from the process table.

These machines happen to be maxed out with RAM and two quad-core CPUs.

How would VM performance differ to a machine with 8 GB RAM and two dual 
core CPUs?

I have users who have been known to bring a physical machine or cluster to 
its knees due to intensive CPU/RAM processing - not bad code, just the 
product of their code.   How will a VM world possible help/hurt their 
efforts?   I don't believe they will be making any specific CPU 
instruction calls, for what that's worth.

Thanks for your insights.

Scott