Selection from List Box to Text Box

Hello,

I have a multi select list box, and I would like to have each selection the
user selects to show up in a text box separated by commas. I have read
enough and I know that its "Evil" to store more than one piece of data in a
field. This textbox is a notes/memo field, and is only being used as such.
I'm thinking that this would happen in the AfterUpdate Event of the List Box.

Does anyone have code that would help me out, or can someone point me in the
right direction?

Thanks.