What format is the file currently in? Text file could be plain text, rich text, MS Word, etc.
For plain text, if you're not afraid of the command line you can look at the
csplit command (do
man csplit for info), or if you want to get really geeky, I'm sure
awk can do it.
Example of csplit
Code:
csplit -f Chapter_ -ks book.txt '/^Chapter/' {25}
The 25 at the end designates how many chapters there are. You can set it higher than you need to be sure it gets them all, though it will output an error message in Terminal, but all of the files will be split.