thanks for all your suggestions, and advice.
In the end, good old HJSplit
did the trick for me.
The last time I used HJ Split, it was a DOS command line executable only. (...and I was running the latest version of Windoze (3.11), on my state of the art 486DX33!)
The latest version (2.4) allowed me to specify the size of the chunks to create, and the file played just like the original when joined. All with a few mouse clicks!
What a great utility!
I downloaded a few of the suggested programs though, and I will have a bit of a play around! (when I can get the time