I assume you've figured this out already, but just in case:
The VBE object tree is exposed through automation - just get the application object for whatever Office file you're dealing with via a CreateObject call, then do the same thing you did in VBA (with appropriate changes from VB6 to .net, obviously).
exl = CreateObject("Excel.Sheet")
exl.Application.Workbooks.Open("whatever.xlsx")
'exl.Application.VBE.ActiveVBProject etc etc