Meet George Jetson (3/6/2013)
I would agree with foxxo, in that a reinstall would be the most simple solution.However, if you are up for a taking a risk, I recall the location of the SQLAGENT90.EXE path is located in the registry.
Thanks
A reinstall is not really on the cards right now - I have managed to find the key in the registry where the path to SQLAGENT90.EXE is kept. I have made the change on a test system and it seems to work without any issues.