you checked 2238 config? theres choice to choose which button, and theres Shift, Ctrl and Alt buttons, untag them and choose only one of them (for example tag Ctrl and choose X button to shoot Groin) i doubt youre noob but check that twice if you did... and Save the setting.
To use autoaim (no matter which OS you're using) you need to set it in Fo2238config.exe (as described above), launch game, choose the part of body, which you want to aim and not to forget, that this feature is only working if you are shooting in a single, non-aimed mode. If you did everything correctly, you shot get a message in the left top corner: If it doesn't help, download a fresh client and update it.