In Microsoft Office 2007, Quick Access Toolbar definitions are stored in .QAT files that are stored in the c:\users\<username>\appdata\local\microsoft\office\ folder for each user. For Office 2010, these are files that are formatted the same but have .officeUI extensions. Actually, you can rename the extension of .QAT files and they'll work with 2010.
If you want to retain Quick Access Toolbars, keep a backup copy of your QAT or officeUI files and copy them to the user's appdata file on a new system.