I have a 2 combo boxes... filled with numbers 1 to 10. How can I do
this.

when a person selects a number from one combo box if should be
checked in another combo box if that number was selected, if it is not
selected let the person select it and dispay a message "the element
can be selected"....

so, lets say I select "2" from combo box 1. Person should not be
allowed to select "2" from combo box 2. When a person select "3" from
combo box 2, a message should pop up.