I have read the system requirements, etc. but all is a little too general for me when we're talking about varying ranges of mailboxes. I am hoping for some 'real world' or 'test' experience for what works best!

We're looking at possibly deploying Zimbra Pro NE with 2 domains, Mobile support, and currently ~ 60 mailboxes total with up to 100 this year.

We would probably working with 1 or 2 Dell PE 2900 III's with dual quad-core Intel Xeon 5410 2.33GHz processors, 4GB Ram, 4 500GB SATA HDD in a RAID 10 (1TB) running Ubuntu 6.06.01 LTS 64-bit. Average mailbox would be 1-2 GB. Migrating from Outlook 2003/2007 PST's.

Would the above be sufficient hardware?
What are the (dis?)advantages to having a multi-server (2) setup versus a single server?
What about single server and cold standby server? (Supported under NE?)
Any other recommendations/suggestions while we consider this?

Thank you to everyone in this community. You are all very knowledgeable. I have followed the forums for ~ 6months and have learned a great deal about what to expect from reading lots of posts, without having run the software at all!