Reynolds, ive only ever managed to delete text/voice. File got corrupted every time i tried to add text.
To remove, SELECT the part of the film you want to edit. (START SELECT and END SELECT). Then click on the "Edit Text/Voice" button and check the boxes according to what you want removed. OK.
I would record the FRAPS avis without sound and add the engine and fire/damage sounds manually in the WMM. Thats a lot more work on the audio track, but you can make it a lot more realistic and accurate that way.