Question: Can I upgrade my existing Exchange servers to Exchange Server 2010 using an in-place upgrade?
No. There is no in-place upgrade available for Exchange Server 2010. You can migrate to Exchange Server 2010 from an existing Exchange 2003 or 2007 organization, but the migration has to involve a transition of services and data from the existing servers to the new servers.
For Exchange Server 2003 environments the most obvious roadblock to an in-place upgrade is that Exchange 2003 is a 32-bit server application whereas Exchange 2010 requires 64-bit server hardware and operating system to function.
You may wonder why it is then not possible to upgrade Exchange 2007 servers to Exchange 2010, given that both run on 64-bit servers.
The database schema in Exchange Server 2010 has been changed from that in Exchange 2007 and earlier versions to allow greater storage performance. In an in-place upgrade this schema change would be very difficult if not impossible to implement successfully. In contrast a server to server migration of mailbox data allows the data to be written to the new database schema safely and efficiently.
Although the cost of upgrading to 64-bit server platforms may seem like a barrier to uptake of Exchange Server 2010 most customers I have worked with have either embraced the opportunity to replace their aging Exchange hardware with new servers, or have worked Exchange Server 2010 into their virtualization infrastucture.