My 03 i35 didn't come with a navi but i was able to get my hands on a stock navi from an 04 i35 and was wondering if any one had done it and could give some tips.

 

Search the 5th gen forums there's quite a few threads asking the same question. Basically the factory Nav is slow and cd based and the general consensus is you'd be much better off going with and after market nav. If you are determined to do it be advised that it won't be easy.