I tried using Robert's guide for transfering mp3 files to iTunes using iTunes 5.0.1 and MP3 Merger.
The audiobook I have on my HD is 185 files long, mp3.
It's all in one folder and numbered sequentially.
The source was 10 cds ripped to mp3. So the files look like:
01-01, 02-01, 03-01, etc.