Try something like this:
Code:
Sub Test()
Dim x as string
x = InputBox("Enter the column you need inserting, eg "a")
Workbooks("yourworkbook").worksheets("theworksheet").Columns(x).Insert
End Sub
Create your button, link its code to this sub, and you're away. Obviously, you will need to alter the names to suit application, and you will need some way of ensuring that the input is valid, but this is left as an exercise for the reader ;)
HTH
There are two secrets to success in this world:
1. Never tell everything you know