Customers should examine their application and hardware environments closely to see which would be the best fit for them. "It really depends on the environment," Schuster said.

She did have some advice for customers depending on what OS they are currently running, and whether or not they have begun migrating to Vista already.

For customers still running Windows 2000, "they clearly need to move fast and need to move to Windows Vista," she said. Extended support for Windows 2000 ends in April 2010, and it will take a company 12 to 18 months to complete the upgrade. "They can't wait for Windows 7," Schuster said.

For companies that are halfway through a migration to Windows Vista Service Pack 1, they should continue that migration as planned, she said. However, if a company has begun piloting Vista and is not yet halfway through the migration process, moving to Vista Service Pack 2 -- which should be generally available in April -- is a better option.

Some customers have already said they plan to wait for Windows 7, and Microsoft is not recommending they change that course.