We mainly discuss using the managed ObjectARX API here, not the VBA/ActiveX API.
Your question about SendCommand() has the same answer regardless of what programming langauge you're calling it from, and has been asked and answered dozens of times in the VBA newsgroup (hint: search that newsgroup on the keyword "handent").
It may be called the VBA newsgroup, but it would more accurately be called the ActiveX newsgroup, because many topics about that API are discussed there, including those related to using it from standalone VB6 (not VBA); Delphi; C#; and other ActiveX-enabled development tools.
AcadXTabs: MDI Document Tabs for AutoCAD 2008
Supporting AutoCAD 2000 through 2008