combobox-transperent

Hi,
I need information about how to make a combobox items transperant.

I've observed this in address bar of IE in windows vista. Iam much
fascinated to reproduce the same for my windows form. Is there any possible
way so that the items in combobox will have a transperant background.

I tried to do this using "Opacity". but I could get the transperancy in the
selected item of combo box instead for the whole dropdown list.

Also, is there a wa to reproduce the windows forms tree view look like it
does in explorer. I believe its a treeview....

Thanks in advance.