If you are really interested all you need is a text/xml editor. I suggest Visual Web Developer Express (free at
http://msdn.microsoft.com/vstudio/express/downloads/). And if your looking to create images, like creating velious ui would require, you would need a paint program of some sort that supports alpha layers,
thegimp.org is a free one comparable to adobe photoshop.
After that just dig through the xml file in a text/xml editor, read the AboutSIDL.doc in default directory, take a look at SIDL.xml and study it. Then work on small easy stuff at first like adding a gauge here n there, a label, button, until you grasp the xml structure enough to actually do something with it.
It really isn't all that hard, xml is a simple high-level markup language, and most of the eq control properties in the xml files are very straightforward and aptly named.