KB Article: http://support.microsoft.com/kb/2642495
When attempting to install applications you may receive the following error:
"The Windows Installer Service could not be accessed. This can occur if the Windows Installer is not correctly installed. Contact your support personnel for assistance."
For this issue on Windows XP or Windows Server 2003 see the following article:
315346 (http://support.microsoft.com/kb/315346) Error message when you try to add or remove a program on a computer that is running Windows XP or Windows Server 2003: "The Windows Installer service could not be accessed"