Hey Joshua,
To support the large number of users visiting our site, the hosted demo is running on a load-balanced-cluster of 4 machines. They all talk to the same LDAP server, but they're not clustered in the high-availability (HA) sense (because the data in the demo accounts is temporary we're not afraid of losing it.) We WILL be doing true (HA) clustering in the near future.
Each hosted demo machine is a dual opteron 246 with 2GB RAM and 6x73GB in a RAID10 configuration. So in other words, decent servers but nothing too fancy.
The main bottleneck for Zimbra (or any other email system) is disk I/O: to support a large number of users, you want Zimbra on as many physical spindles as possible.
Your system sounds OK for trying Zimbra, although I think our official minimum recommended RAM is 512MB. If I were you I would give it a shot and see how it runs on your box.
- Ari |