Hi Steve,
Base on your description, you want to add the menuitenseparator for the menuitems, right?
In asp.net, it work not like in the windows menu, but you can implement it to make a picture is a horizontal line, and add it as menuitem's the SeparatorImageUrl. So it will looks like a MenuItem separator.
Hope it helps.
Please remember to mark the replies as answers if they help and unmark them if they provide no help.
Yours sincerely,
Amanda Wang
Microsoft Online Community Support