Listbox question

[sonic]

Hello,

Can somebody help me with this (if it's even possible)

I like to have a multiselect listbox with some items (of course) like: one,two,three,four

the items selected have to be stored with some kind of seperation mark (eg ',' )

Also a editbox for entering extra information, this has to be stored in the same way.

If possible than the information in the editbox should be used the next time the listbox is shown. So it has to be added to the list. So if i add seven to the editbox, the next time the list should be: one,two,three,four,seven

Thanks for reading this and any help