One of the quickest ways to get a feel for XSLT is to use Internet Explorer*. It will transform XML based on a defined style sheet so you can quickly check the effects of a specific XSLT on your DOM. I'd recommend going through the
specification having a play with the various transformations you can do. I find having a much more immediate method of seeing what can happen helps me speed through XSLT development.
(*You can of course also get
IDE's that support XSLT, but IE will do fine when you are just learning)