The other option is to go with a hosted option where someone else maintains the hardware while you admin the Zimbra software.
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Culley
Mail | Dell 2950III | 2x Quad Core 5420 | 8gb RAM | 6x 146gb RAID 0+1 | Red Hat 5.3 | Zimbra 6.0.1 Network Edition
Test | HP DL360 G3 | 2x Xeon 3.06ghz | 4gb RAM | 6x 18gb RAID 5 | CentOS 5.3 | Not in use now |