The Exchange Team (AKA you had me at EHLO – actually had a customer groan at that name the other day) have released a calculator to help you work out the storage requirements for your Exchange 2007 servers.
Other useful links include
- Storage Requirements Blog - http://msexchangeteam.com/archive/2007/01/15/432199.aspx
- Processor & Memory Requirements Blog - http://msexchangeteam.com/archive/2007/01/16/432222.aspx
- Understanding Exchange Server 2007 I/O improvements from 64 bit - http://msexchangeteam.com/archive/2006/09/08/428860.aspx