faster111, you need to get a sound editing program that can import/export .RAW audio files.
All the horn files are located in the \LFS\data\snd folder as:
HORN1.raw
HORN2.raw
HORN3.raw
HORN4.raw
HORN5.raw
You can replace the sounds there, but you need something that can handle RAW sound files. I can't recommend any, so search for some online at Download.com or something.
I get a problem with edited sounds. When starting LFS, it says the sample rate is not supported. Ive tried like 5 different sample rates and I dunno what is supported!
I usually find 44100 Hz works fine, saving it as a signed 16 bit mono .wav.
Hughie. If you really can`t get your sounds to work then post them here if they`re not too big, or PM me if you don`t want them public and I`ll help you get them fixed.