Increment Text Column Reference ("AZ" -> "BA")

I'm setting up a workbook where users will select a saved workbook from a network drive (using Application.Dialogs(xlDialogOpen).Show); the macro will then open the selected file and pull data from select columns in that workbook and paste it into the summary workbook which holds my code.

The column into which the data will be pasted will vary by source workbook, so I'm using application.inputbox to have the user provide the first column into which data should be pasted for the selected workbook. Each workbook will have data that needs to go into two side-by-side columns, so rather than asking the user to input another alpha column header, I want to just increment the original input to represent the next column, so I can use that in my code.

Since the data is coming in as text, does anyone have an eloquent way to increment it, taking into account the rollover each time the final character is 'Z'? I thought about defining the inputbox variable as a column and using offset, but that isn't an option in the dim/as autocode. This code will primarily be used in Excel2007, but ideally would also work in 2003.