RE: MP.MSI exited with return code: 1603
When experiencing errors as per those that you are reporting above, I have found the following to work quite reliably:
1. Disable all services that:
Relate to Anti-Virus Software.
Relate to Backup Software.
Relate to management agents (ie: OpenView, Systems Insight etc).
Relate to ANYTHING that might be using IIS. MP.msi wants to restart IIS components - if any running services/software are interacting with/depending on IIS your MP install is sure to fail (eg: MS Exchange Server).
2. Restart the system.
3. Assign MP role and wait for installation to complete.
4. Re-Assign modified service startup properties back to original values.
5. Restart system.
Essentially, MPSetup/.msi and the associated routines that it calls are extremely sensitive to anything that they may interact with. Configuring your site server to be running basically only the OS+SMS (as per above) is the best state in which to attempt to install MP role. If this should fail then by all means re-install IIS etc.