If you wanted to build your own dstudio and you wanted to 'get around' getting x/y/w/h utilizing something in mIRC, you can create your own. Say you have your own DSTUDIO and you have a canvas for it where the user builds the objects on the dialog. When they drag/drop, use something like a 'box' with no caption and have it follow the users' mouse across the screen until they let go. When that happens, just store the X & Y begin points and then store the W & H by calculating the positions and offset the width from where it started (W by X and H by Y).
After you do that, you can utilize a customized $identifier, so you could, in a sense, create something like: $didobj(ID#,x/y/w/h). In this case, you would store dialog object ID's into an ini file, or a hash table (which ever you'd prefer). Next, when a user wants to move an object, UNFORTUNATELY, you won't be able to drag/drop at real-time on the dialog, but when they click on the object, just use $mouse.x/y on the dialog and check to see if the x/y is within the location of a certain object. This is the hard way, unfortunately. Actually, a way around this would be to just use the ON DIALOG sclick events on ALL objects in a temporary dialog that you've created.
However, this WILL get tedious because you would have to load/reload/load/reload the dialog that the user is working on OVER AND OVER again. Anyhow, have fun! :-)