Microsoft announced a deal on Friday that lets customers who buy Office 2007 between now and Sept. 30 to receive a copy of Office 2010 without any extra charge when it becomes available this spring. However, a little-noticed item in an FAQ for what Microsoft (NASDAQ: MSFT) terms its "tech guarantee" for Office 2010 provides a cautionary note that many users and IT staff will want to be familiar with.

Specifically, if a user installs one of the 64-bit editions of the next Office version, many existing 32-bit Office add-ins will no longer work, according to the FAQ.

"We strongly recommend most users install the 32-bit version of Office 2010 on both 32 and 64-bit Operating Systems because currently many common add-ins for Office will not function in the 64-bit edition," the FAQ said.

That is not to say that users who feel they need to run the 64-bit editions will not be able to get them.

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