Form Validation Check For NULL?

I am putting some validation on some forms at work. The users have asked to put something in place to make sure that if you enter something in on field that you must enter something in the corresponding field.

Example : Lets say there is a Company field and a Position field. Well they would like that if you enter a Company you should enter a Position and the other way where if you enter a Position you just enter a Company.

Ok so thats easy enough I did something like the following.

if((form.Company1.value=="") && !(form.Position1.value=="")){
alert("Enter a Company into the Company field for row 1 or enter N/A");
form.Company1.focus();
return false;
}

Well now they want a message box to give the user the option it ignore that they have a blank field, and more or less want a �hey just to let you know, you didn�t put anything here