There is a way to install Microsoft Office 2010 while keeping Microsoft Office 2007 also installed.
Run the Microsoft Office 2010 setup wizard and click Customize rather than Upgrade.
Click browse to choose a different installation folder than that which already contains Microsoft Office 2007. Choose a new path such as
C:Program FilesMSOffice 2010
By choosing a different installation folder you will now be able to run both Microsoft Office 2010 and Microsoft Office 2007 at the same time, or individually, but maybe not while opening the same file. Outlook 2007 will be uninstalled however, and replaced with Outlook 2010, but it can be spared by simply choosing not to install Outlook 2010 during the setup process. If you have the retail version, and not the testing beta version of Microsoft Office 2010 then there is no reason not to replace Outlook 2007 with Outlook 2010.
The Office files will be linked to Microsoft Office 2010 after installation, but you can changed that in the Control Panel, or by running the Office 2007 setup wizard, and choosing to Repair the installation.
If you are running the Microsoft Office 2010 setup from a folder on your hard drive you can also download the pre-configuration filed config.MSP that will install Microsoft Office 2010 while preserving Microsoft Office 2007.
Once the config.MSP file has been downloaded, copy it to the Microsoft Office 2010 folder that contains the Setup.exe file. Next open a command line prompt window as administrator and type:
SETUP /adminfile config.msp
(For instructions on opening a command line prompt window as administrator click here)