UserForm - Summarize Unique Values from Two Columns

Hi there,

I am quite terrible with Macros/VBA, and have recently purchased a sizable tome on the subject. In the meantime, I would be most appreciative for help on the following:

Scenario:
I am trying to create a UserForm (or similar) that summarizes the non-duplicate values from one column compared with another column. This summary is to have the option of selecting the values, and then have them added to the primary list.

Detailed Request:
The UserForm (or pop-up) is to list values that are in Column B, but not in Column A.

The UserForm is to have a check-box (or selection method) next to each listed value. The number of values will vary, and subsequently so must the number of check-boxes.

The UserForm is to have a button.

If check-boxes are checked, and the button pressed, the checked values are to be appended to Column A.

The UserForm window will only appear if values exist in Column B that are not in Column A.

Thank you for your help, and suggestions,

Yaddles