bionioncle, sry... as far as I know, the contact list can only hide to the tray or left/right side of the screen...
addition:
you could go Options->Contact list->Window->Disable Skin engine or Use non-layered mode
and also activate "Show title bar" so you'll get the taskbar icon... though you'll end up without skins for the contact list.
It'll still hide into the tray, so you shouldn't "close" it.