That Derek. He's such a holdout.

Don't manually type any xml, unless you have to.   You can easily create xml using any number of tools (Visual Studio Express is free and is what I use), you can generate a schema for the various xml files if it is something that you need (use the xsd.exe tool from microsoft), otherwise they are fairly straight-forward to generate from c#/java classes if you are familiar with xml structure.

edit:  I should note that the one exception to the "straight-forward" comment I made is the quest xml which is complex and not very easy to model.   I started a Quest editor and ultimately decided to wait for the super spreadsheet we are going to get from Derek.   It is possible to create the editor, it would just take more time than I was willing to spend on it.  

Let us know what particular area you are interested in, and I am sure you will find plenty of folks willing to help out.

Me too. Very quick and fewer errors. 

May I humbly suggest Notepad ++ for those who don't want to use VSE. Notepad++ even has tabs for remembering documents! Very useful, there is also a compare plugin for those of you who are working on a quest and want something to diff with. However, since the lines will not be exactly the same, its a little buggy, but might help you get an idea of why something is broken.