Hello
The command to load descartes if you have a Microstation session already open is MDL load dcartes.ma. Is there a way to create a macro or button that you can place on your Microstation screen, for people to press if they wish to open Descartes?
Yes, you can easily create buttons to load and unload Descartes. You need to create a *.dgnlib file in ...\WorkSpace\Interfaces\MicroStation\[your interface directory]\. Then, open this *.dgnlib in MicroStation and you can create new buttons in the Customize dialog (Workspace > Customize) using the MDL LOAD DCARTES and MDL UNLOAD DCARTES key-ins. Search for "Customize dialog" in MicroStation's Help file for more details.
HTH
Pascal
In addition to Pascal's suggestion, you could add the keyins to a pair of function keys.
To do that, go to Workspace > Function Keys.
Select a key and add mdl load dscartes as the action on one key and mdl unload dscartes as the action on another.
Save the changes.
For addtional information search Help for "Function Keys".
And you'll also find some stuff in this article:
http://communities.bentley.com/Communities/Other_Communities/AskInga/w/AskInga/all-about-function-keys-and-function-key-menus.aspx
~Inga