I can't even recall how I did this, but it wasn't particularly difficult. I didn't have any special tools, so they aren't really necessary (or I was very lucky).sbhatia said:
If you search on my name you ought to find a thread on nav retrofitting that has a link to the DIY that I used.
BTW, I ended up with some screws left over; apparently the nav screen doesn't use as many as the non-nav setup.