I'm planning to buy HP server ML350G5 (QC X2.0/6GB RAM, 4x146GB HDD, DVDRW). It will be used as test lab for virtual Windows Server 2003/2008 installations.
What I didn't decide yet is if to use ESX, ESXi or XenServer. Are there any known issue with above hardware? What is in general better virtualization server to use? I have basic knowledge about ESX, but I'm open to learn new stuff.