http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/c741ec26fa674b1e8825738a0076abf3?OpenDocument
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"
http://support.microsoft.com/kb/q315346/