I'm currently running on a TravelMate 2700 3GHz P4 with 80 GB HDD 1.2GB ram with 70 users on CentOS 4.3 Pretty scary huh? It was actually a stop gap measure when the "real" server died but I've been very pleased with the performance with such inadaquate hardware that I can't wait to see how it does with a couple of Opteron 280's, 4GB ram and 3 Rator 150 GB drives in a raid 5.
I'm a little worried about loading them with the 64 bit version of the OS, is it true that Zimbra will fail if I try?
I'm also considering using a simpler setup with an Athlon X2 4400+ and a larger SATA (II) 3 Gb/s on the back end with 3 Travelmates on the front end, but I'm not sure what kind of horse power I would need for a load balancer like Ultra Monkey. Lotsa laptops but not alot of capitol for hardware.