comparing two fields from different forms

I have two forms in which I want to compare a field from each. The two forms are linked through an ID #. The problem is that I have no idea on how to compare the two. I am fairly new to programming with VB and have been referring to examples from books to aid in the process thus far. Can anyone give me any suggestions? Below is some information that may be helpful:

The two fileds being compared are:

CLASS_TIME (form)
CLASS_TIME (subform)

The field that links the two forms are:

STUDENT ID


I'm simply trying to generate code that will inform the user that the CLASS_TIME in the form, conflicts with the CLASS_TIME in the subform. Any suggestion will be gratly appreciated.

The easiest way that I can think to do this would be to just reference the classes explicitly...

if form.CLASS_TIME <> subform.CLASS_TIME then
'some code
end if

This should work, however both forms must be open to do this process.