To save writing my own "Create Material" form I though I would try the line below.
acDoc.SendStringToExecute("Materials ", True, False, True)
However, when called from my form, the command does not execute till I end my command (I'm inside a form called from another form and the command doesn't execute till both forms are closed)
There has to be a better way of doing this, so I can leave my forms running.
P/Invoke acedCmd() function from ObjectARX: http://forums.autodesk.com/t5/NET/acedcommand-func