Dreamweaver has some simple support for XML (especially Dreamweaver 8). There are also very powerful XML tools such as
Oxygen. Eclipse also has XML support.
What errors do you get? As long as you use valid XML, I don't see how you could get errors saving and reopening the file.
As a side note, XML is awesome. Anybody reading this thread who doesn't know XML should learn it immediately. I'm using XML for a new project at my web site that will blow your mind (I am not modest). Hint: with XML, you can publish information from vBulletin to any other application that supports XML parsing. And yes, you can create XML in PHP:
http://www.php.net/dom .