Combobox Multiple Selection or Listbox Dropdown

Hi all

I have a userform where I want the user to be able to select multiple options, but am having a bit of a problem finding the best way to do this. If I use a combobox, I don't appear to be able to allow multiple selections, but if I use a listbox I don't appear to be able to implement a dropdown facility. I would prefer to have a single line sized box on my form, but doing this with a listbox would probably be confusing for the user as it is not very easy to see what has been selected.

Can anyone offer any advice on a good way to do this?

Cheers

Matt