The server hardware sounds pretty good, I would try to increase the RAM if possible. Your 5 NT boxes will run fine with 8 GB but going forward you'll want/need more. If necessary, dial down the proccessors. Two Quad-Cores per box should be plenty. Especially if they're the new Nehalem procs. The other issue you'll run into is that almost any ESX feature will require you to have the VMs on shared storage. Either a SAN or NAS with FC, iSCSI, or NFS. HA, DRS, DPM, or FT won't work with the VMs on local storage. My reccommendation would be to scale back on the 1TB of local storage and go with a mid to high-end NAS.