The only tutorial I know of for Desktop X is by Martin for DX v.1.0 and is located here: https://www.stardock.com/products/desktopx/tutorial/default.htm It has not been updated for a while, but it might still be worth a walkthrough. Have you checked the guides for DX2? https://www.stardock.com/products/desktopx/resources.asp I have found them to be quite useful - even more useful since I printed them out and began making notes in the margins. They are written in PDF so in my opinion they are much easier to use in hardcopy.

As for Object Dock, I don't use it myself so can't help much there. Regarding Sysmetrix, I don't know of any tutorials, but the manual that comes with the program is pretty good. The best way I have found to learn how to skin Sysmetrix is to load a theme that has features you like, and then play with the configuration. The config GUI for Sysmetrix is really a great teaching tool in my opinion, as it allows you to see almost every aspect of the program, and you can see you changes happening in real-time on the theme. (Provided you don't have the config window cover the theme of course... )

BTW, the new development build of Sysmetrix is available for download at Xymantix' site: http://www.xymantix.com/sysmetrix/development.html and is definitely worth checking out. It adds a lot of new features over version 3.0.