Try XML Spy v3.0 via softwareblast.com. Of course, I wouldn’t tell you there there is also a crack available for this. That’s not the kind of thing we do around here. This is not the end-all-be-all evironment for learning XML. But, it will give you a place to start with a nice set of help files.
Other places are almost far too numerous to mention, it’s best to hit Google with the keyword. That’s going to give you a list of reading that will take you weeks to get through.