KB article: http://support.microsoft.com/kb/290301
Sometimes you cannot uninstall the existing 2003, 2007 or 2010 Microsoft Office...
Sometimes you cannot uninstall the existing 2003, 2007 or 2010 Microsoft Office suite on your computer by using the Add or Remove Programs feature in Control Panel of Windows XP or the Programs and Features feature in Control Panel of Windows Vista if one of the following conditions is true:
- The installation process did not complete when you tried to install a new program. Therefore, you are left with a partially installed program. When you try to install the program again, you are unsuccessful.
- A previously installed program cannot be removed because the installation files are corrupted.
- If you had problems installing Office 2010 from a previous attempt.