1) Click on the start button
2) Click on 'all programs'
3) Right click on 'startup'
4) Click 'open'
5) Now LEAVE THIS WINDOW ALONE and in a seperate window find the name of your theme. It is PROBABLY easiest to open DesktopX and click on 'Load desktop' but importantly DO NOT double click on the desktop you've been creating
6) Drag the desktop you have been creating from there, into the startup window we made earlier
7) Thats it! Ensure that these files are 'associated' with desktopx. This is the middle tick of the 'desktopx builder' preferences - make sure it is ticked and 'apply' is hit.
You see rather than opening desktopx builder with some kind of parameter specifying which desktop you are after, I am simply putting the DESKTOP FILE NOT THE BUILDER PROGRAM into the startup and then letting the OS think 'aaah - this file is associated with DesktopX builder' and loads that up with the desktop you want. EXACTLY THE SAME as if you put a microsoft document into the startup it automatically knows to load 'Word', if you get me.
The LAST bit of the jigsaw is when you boot it will say 'Do you want to save desktop before loading 'whatever.desktopx' and you just click 'no'. I'm working on a way to disable this dialog box now for 100% solving your problem ...