You can install pdftk and do it from the commandline.

Split large pdf into many one-page files: pdftk largepdfile.pdf burst
Merge files into one PDF file: pdftk *.pdf cat output onelargepdfile.pdf

There are many more commands that will do more things. Try: pdftk --help

I think that ghostscript will also do the trick, but have never used it.
There is also PDF Split and Merge which I have never used.
www.brighthub.com/.../14795.aspx
http://www.youtube.com/watch?v=eQoOk5Xbt3M

I have used this a long time ago. I am not sure if it will still work:
sourceforge.net/.../

Good luck. Please report back. I have not done this in some time so am
interested in your results.