XML transformation

I'm sorry if this question is a little bit on the edge of what this list 
covers - it's just I know that there are some XSLT gurus on here
and it is to do with conversion between W3C schemas.
 
I have an XML document that complies with one schema and I 
want to convert it so it complies with another. I understand the 
semantics of both schemas and the transformations I wish to
achieve. Will I, in all cases (and given a good knowledge of XSLT) 
be able to freely convert from one to another e.g omit elements 
conditionally on values of others, combine elements and attributes
and anything else whacky and arbitrary. What I'm really asking is:
will I be able to do everything that I could do in C++ with XSLT. 

I'm prompted to ask this question because I heard that XSLT 
is a functional language but I don't know what the practical 
implications of this are. Does it mean that it is Turing 
incomplete like XML schema language? If so, does this mean
that there are certain things I cannot do and if so what sorts of 
things.

Does anybody know of any tools that ease or partly automate 
the process of producing transformation stylesheets; I've heard
that XSLT is pretty hard to get started with.

thanks
Gaz