It should be at- Start > Programs > Microsoft Games > CFS2 > CFS2 Mission Builder & click that, it's worth making a shortcut & keep it on the desktop, i dont know which OS your'e using, in Win98 you just do the above & instead of left clicking CFS2 Mission Builder you RIGHT click it & select 'create shortcut' from the menu & it should appear on the desktop.
If this does'nt work open Windows Explorer & find Microsoft games folder & click on the mission builder exe there.

Happ