Is there wiki code to be able to open links in a new window(external links)?
No, this has generally been considered to be a Bad Idea, since this should be up to the user and their browser-interface, rather than the website they are viewing. (I believe shift-click, ctrl-click and the middle mouse button allow users of some browsers to open a link in either a new window or a new tab).
Although I agree with you, a recent discussion on the CHI-WEB list brought up the fact that it seems as though opening external links in a new window is a growing trend and may someday become the expected behaviour. I never win.