Running A Macro When A Certain Value Is Found Anywhere In A Certain Column

I’m working in Excel ’03 with a large table. I’m hoping to run a macro against a cell with value ‘X’ whenever that value is found within a particular column. I’d like this to be relative and not tied to a particular column so I can tweak it as needed down the road and run it against different columns.

In the example below, lets say I’m working with column B. I’d like something that would go through every cell in the column and run a macro when it comes across a particular value. Let’s say this value is x.

__A B C D E F
1 a x a a a x
2 b a b b b a
3 c x c c c c
4 f f f x f f
5 s s s a s s
6 g x g g g x
7 a a a a a a
8 s s s s s s

So, in my example, the macro would be run on B1, B3, and B6. And, if I wanted to go back in later, I could run this on column D and the macro would run on cell D4.