Hi Butters,
You could try Altova XML spy, which is the XML software I use at work. It has the ability to load in an XML file and convert csv, though I've never tried it with very large files.
You'll also need to download Altova Map Force 2007 to complete this task.
It cost quite a bit to buy, but you can download a 30 day trial version which should contain all the features you need.
If not reply to this thread and I'll give you my email address and I can try to convert it for you, unless it has sensitive information that you don't want anyone to see.
Good Luck
Taff