VBA code should be almost 100% compatible with VB 6 code. The main
differences are that VBA gives you the Application object and in VB you'd
need to instantiate one (or more precisely use the trusted Application
object passed in the On_Connection event). Any forms you created in VBA
would use VBA UserForms, in VB they'd use VB forms.

I recommend that you download the ItemsCB Outlook COM addin template as the
skeleton for your addin (www.microeye.com, on the Resources page), it
provides a framework for you plus workarounds
for many common COM addin problems. You also should review the information
at http://www.outlookcode.com/d/comaddins.htm.