The unit you want is:
http://www.dawntech.hk/di-GPS/pro_1.htm

I have 2 of these units. Tiny. The size of a small box of wooden box of matches and work great! Nothing else comes close.
I've used 3 Garmins and I also have the di-GPS Mini. The a 4 inch cable to your 10 pin connector and your not fighting RS-232 and the long cables or the expense of the Nikon adapter.

I have one each on my camera strap of both my D3 and D300 permanently. This keeps the hotshoe free for the flash. I use the mini to swap around on my other camera.

D3, D300, D2X & D200
New 14-24 F2.8 too!
If your not shooting Nikon your doing
it WRONG!

My Nikonians Gallery