There are some really great tools out their that have xml parsers and everything. One ide that I like to use is XML Spy which gives me a great environment to work with and especially the ability to work with multiple files for the internet, like these types of files: xml xsd xsl xslt xdr svg smil wml rdf xhtml html just to name a few. I also use winedit and textpad. I get to create certain parsing files to use with them.
It depends on what you want to do. Since XML development spans across a process-space you will need different tools at different stages of development
XML/XSL Creation - Notepad, any advanced text editor will do this job. Some of the Java IDEs are now XML-enabled which means you will get nice features like syntax highlighting etc.
XML parsing - you will need a parser. Apache has Xerces. Microsoft and IBM has their own versions. They are all free!!
XML rendering - you will need an XSLT engine( Apache has Xalan and uses Xerces ) to convert your XML to another XML or any rederable format. Internet Explorer version 5.5 onwards has built-in XML support which means you can apply a stylesheet and view the resulting HTML/XHTML/text files using the IE browser. It also checks for well-formedness and xsl syntax, so you can actually use IE as a developent tool. One word of caution - the XSLT support of IE is not complete so you may find some advanced features( like call-template ) not working. Many XSLT engines like xalan support command-line execution and so you an generate the HTML file offline and view the resulting document in any standard browser.
Publishing framework - these are XML-based application that nicely integrates into a Servlet architecture. Checkout Apache's Cocoon( www.xml.apache.org/cocoon ). This is not a required tool, but it can alleviate a lot of headache.
score another one for xml spy it can be found at www.xmlspy.com ------------------ I wish there was a button on my monitor to turn up the intellegince. Theres a button called 'brightness' but it doesn't work
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."