I figured it out (I can't seem to fiqure out the Range name technique but as long as I have a range to work with, it goes like this:
Private Sub UserForm_initialize()
'Define the Inventor application and OLE Desriptors
Dim oApp As Inventor.Application
Set oApp = ThisApplication
Dim oOleRef As ReferencedOLEFileDescriptor
Set oOleRef = oApp.ActiveDocument.ReferencedOLEFileDescriptors.Item(1)
'Define the WorkBook and WorkSheet(s)
Dim oWB As Excel.Workbook
Call oOleRef.Activate(kEditOpenOLEVerb, oWB)
Dim oSheet1 As WorkSheet
Set oSheet1 = oWB.Worksheets.Item("Belt_Data")
'Populate the Combo Box
cb_BSeries.List = oSheet1.Range("A4:A30").Value
End Sub