A family of Microsoft word processing software products for creating web, email, and print documents.
Word 2010: File > Options > Proofing > AutoCorrect Options...
Word 2007: Office button > Proofing > AutoCorrect Options...
Word 2003 or earlier: Tools | AutoCorrect Options...
Activate the AutoFormat As You Type tab.
Clear the check box labeled "Straight quotes" with "smart quotes".
OK your way out.