There are quite a few situations recently which have come up where you might want to bypass the MOM 2005 installation prerequisite checker. These include installing MOM 2005 (not SP1) on a Yukon server, installing the MOM UI on Windows Vista, or installing MOM 2005 in a situation where the prerequisite checker does not acurately detect the software installed or hardware.
If it detects a failure to meet a minimum software or hardware requirement, the MOM 2005 prerequisite checker is designed to prevent the user from installing the product and getting into a bad state until the minimum required software or hardware is installed.
In these situations, you can bypass the prerequisite checker by installing from the command line and passing a parameter which tells the MOM setup to skip the prerequisite check. To do use msiexec.exe and pass PREREQ_COMPLETED="1".
See the MOM 2005 Deployment Guide for more details on the required and optional command line parameters.
See MSDN for more information on the msiexec.exe command line parameters.