Thanks TServo2049 for the info
Did not know about that dvd but seems to be hard to find
after my original post i stumbled on this streaming version which has the original music, its 64kb stereo mp3 but sounds good enough for me so im going to try and sync that with the hd video
http://onlineshortfilms.net/watch/wallace-and-gromit-in-the-wrong-trousers-video_f4749ca87.html
downloaded it with downloadhelper in firefox then ripped the audio with vlc for anyone who wants to do the same thing