ISA Server & XML Destination Sets

Help!
I'm using a no_porn destination set of approx 20 MB written in XML, downloaded from www.toolzz.org. It is effective but is giving me some problems.

I want to chop it into 4 smaller files with IP addresses separated from URL ones.

I can't.
MS XML Notepad and other XML editors take several hours trying to open the file and then fail.

I use an Athlon XP running at 1.2GHz 1 GB of RAM, loads of disk space and Win2K SP2