OGAAddin.dll (and OGAVerify.exe) is a few files that been installed by OGA Notifications. OGAAddin.dll allowed OGA Notifications to install as an add-in to applications in Office productivity suites to display not genuine reminder message to illegitimate and illegal copy of Office. By stopping the OGAAddin load behavior and preventing OGAAddin.dll from loading, the Office Genuine Advantage Notifications message can be suppressed.
This fix worked for me on Windows XP w/Office 2003. There are other ways to accomplish this that may be required if using a different version. See the link below for other options.
Note: originally posted here.