Jim,
Making the second form do this seriously breaks encapsulation. Why not just structure you code like this:
DO FORM AddVendor (assumed it's a modal form)
this.cboListOfVendors.Requery()
If the AddVendor form is not modal you could pass a reference to the form to the other form when you launch it. Then the other form can send a message back to the first form:
DO FORM AddVendor with thisform
AddVendor.Init:
lparameter roCallerForm
this.oCaller = roCallerForm
then when you want to inform the other form of the changes
thisform.oCaller.UpdateVendors()
>How do you reference a combobox on a form that is not the active form? I open a new form to add a vendor and want to requery the combobox so it has the updated vendor, but it is on another form that is present as soon as I close the vendor add form. I have always used thisform.etc.etc, but what do you use if it is not on thisform?