Hey, over the past little while i did a ton of research into remote shutter release for my Nikon D5000 and couldn't find anything. Today i found 2 products that are said to work. The first is an adapter allowing you to use the standard 2.5mm Canon Bite/Tongue switch. 2nd is a Blow switch.
http://pc-mobile.net/nikongps.htm BOTTOM OF PAGE
http://ultimate-switch.com/store/index.php?main_page=index&cPath=2