Here is a complete XSLT reference book although it does not specifically deal with FileMaker Pro:
XSLT 2nd. edition Mastering XML Transformations by Doug Tidwell, http://oreilly.com/catalog/9780596527211/
Beverly Voth's book may help. Its for FMP6 but considering the XML hasnt changed, it may be worth a read.
Thank you for those suggestions,
I've found the O'Rielly book in the library.
The FMP6 book looks quite interesting and probably better to my immediate interests, if I can find it.
There is an e-book version I believe as well.