Install Now This option appears if you do not have an earlier version of Microsoft Office installed on your computer. This option allows you to run a complete installation with the exception of a few specialized files.
Upgrade This option appears if you have an earlier version of Microsoft Office installed on your computer. This option allows you to run a complete installation with the exception of a few specialized files. The earlier version of Microsoft Office detected on your computer is automatically removed.
Customize This option allows you to make specific choices about each aspect of your installation, including which programs are installed, and where they are installed. For example, you might want to install only one program instead of several.
If you receive an error message or encounter a problem, visit The Microsoft Office 2010 Setup Resource Center for troubleshooting information and how to contact Microsoft Product Support.