listbox issue

I've got two listboxes within my vb form, listbox1 and listbox2, and a textbox named Textbox :P

Both listboxes get their values from an xml file, and all values in listbox1 correspondent with the values in listbox2

Listbox2 is hidden, but if I select a value in listbox1 I want the corresponding value in listbox2 displayed in the textbox.

So for example if the values in the listboxes are as following:

Listbox1
tooth
bird
fish

Listbox2
Toothpaste
Wing
Water

And I select fish, I want the textbox display water.
I haven't programmed in vb.net for a long time.. but how can I display the corresponding value from listbox2 in the textbox ? I know it's something with selectedindex, but I can't remember :ehh: