Extensible Stylesheet Language Transformations or XSLT is a language that allows you to transform XML documents into XML, HTML, XHTML, or plain text documents. It relies on a companion technology called XPath. XPath helps XSLT identify and find nodes in XML documents; nodes are things like elements, attributes, and other objects in XML.
Here is a great XSLT reference with samples I took from a microsoft site and applied a little change tso it also works in the latter IE browsers (doesnt work in FF)
Google the web for many xslt stuff. W3schools is probably your first hit, always a good one to start. O'reilly books are nice. I have some of them.
some more links
A very simple but useful editor to test your xslt transformation is xray (4mb). Open your xml and xslt. All changes are directly applied to the third screen and you can save your workspaces. No intellisense or debugging. A little hard to find the download so also available here download xray
It is easy to find good editors that you need to pay for, they usually offer 30 day trials like xml spy or xslt oxygene. Both offer a nice xslt debug option. Really useful to learn and test your xslt and xpath queries. XML spy is more expensive than Oxygene. I also found another xslt debugger which runs on the java framework (need to download that from sun). This one is far less easy to use but once you get it it works quite well on debugging and is free to use in non commercial environments (like learning at home). Check http://www.freexmleditor.com.
Another alternative which I've not tried yet but which is low cost http://free.editix.com/.
There are more to be found. I like to hear your tips! (you know or can easily guess my email from the url! just change a . in a @)
BROWSER xml + xsl
The way to apply an XSLT stylesheet like msg.xsl to the document msg.xml in a browser is by using a processing instruction. A processing instruction (PI) allows you to include instructions for an application in an XML document.
XSL-FO similar to CSS
XSL-FO is a language for applying styles and formatting to XML documents. It is similar to Cascading Style Sheets (CSS), but it is written in XML and is somewhat more extensive. (FO is short for formatting objects.). For example used to create pdf (fop apache)