Microsoft Word will easily work on documents larger than 48,000 pages (you can create documents of poractically unlimited size). It's best not to exceed 2,000 pages in a single file: although you can go to 5,500 or so if you have a sufficiently powerful computer. The old "32 MB" limit no longer applies: that was a limitation of the file system way back, and applied only to the "text" portion of the file, not the graphics. On 64-bit OS X or Windows you can go way above that if your disk is fast enough.
However, as mentioned by the other poster, it really isn't a good idea to allow a document to get that large. Research proves that the ability of someone to use a document deteriorates rapidly when it passes 250 pages, so at that point, you should be looking to redesign your publication.
It is also true that a 48,000-page document represents 96 man-years of effort, well over ten million dollars of investment. When you have that much investment at risk, it is essential to have at least one highly-skilled Documentation Engineer on the project, because the difficulty of creating such a document rises quite sharply with size and complexity.
Microsoft Word will do documents this size, and so will Adobe FrameMaker. Each of them requires high skills to use effectively on such large projects.
If you care to hop on over to here:
http://www.officeformac.com/ProductForums/Word/
We will be happy to show you how to do this in Word.
Cheers
John McGhie
Microsoft MVP [Word and Word:Mac]