Windows Vista isn't the only recently released Microsoft software that will give users headaches when they upgrade their systems. Corporate users, partners, and analysts said upgrading to Exchange Server 2007 from previous versions also may be a lengthy and painful process for companies, which may want to take a wait-and-see approach to the new software.

New hardware requirements, incompatibilities with other Microsoft software, and the complexity of the product's new architecture are just a few of the issues that will make a move to Exchange 2007 from Exchange 2003 or earlier versions costly and difficult for IT administrators, said Microsoft partners and analysts.

"There are about 6,000 pages of documentation that an IT administrator will have to wade through to deploy [Exchange Server 2007], said Keith McCall, a former Exchange director at Microsoft and now chief technology officer and founder of Azaleos, which offers an Exchange Server appliance and turnkey product. You need to think hard, and you need to plan your server infrastructure to add the value and new functionality of Exchange 2007."

Exchange 2007 is the first major update since Exchange 2003, and it is the first version of the software that runs only on 64-bit servers. Previously, Exchange ran on 32-bit servers, so customers will not be able to just switch out their current version of Exchange to a new one. They will be required to update the hardware.

To its credit, Microsoft alerted customers in November 2005 that this would be the case. But the 64-bit transition is not the only hardware headache associated with upgrading to Exchange 2007, McCall said.

Because of the various server "roles" Microsoft has introduced for Exchange Server 2007, the software can no longer be set up for high availability on two servers -- one for the roles and one for failover, he said. There are five different server roles for Exchange 2007 -- mailbox, client access, unified messaging, routing and hub transport, and edge transport, which filters e-mail before it hits the mail store.

"If you want to run all of the three primary Exchange 2007 roles (mailbox server, hub transport, and client access) with high availability, you need at least four servers, twice as many as you needed in Exchange 2003," he said. "If you want to add the unified message and edge transport roles, you need six servers."

If you don't want high availability, you can run all the roles of Exchange Server 2007 on one server, except for the edge transport server, which requires its own, according to Jeff Ressler, director of the Exchange Server Group at Microsoft. He said Microsoft created Exchange 2007 with these new roles clearly defined because it is easier for administrators to proactively choose which role they want Exchange to play in a network. Previously, they had to go in and turn off the roles they didn't want.

"In the new world, you would choose, 'I want that to be a client access server,' and just install those components," Ressler said.

Hardware is not the only pain point for customers upgrading to the new version of Exchange. Duncan Greatwood, CEO of PostPath, in Mountain View, Calif., said there are some incompatibilities between Exchange Server 2007 and Windows Vista, the new version of Windows that was released to business customers in November and to consumers earlier this week. PostPath has a mail and messaging server that runs on Linux and can connect seamlessly with Exchange Servers on a network.