NAVTEQ stores maps and POI (point of interest, like hospital,hotel,restaurant,bar,.....) in different file formats.
You may add your own POI spot(s) easily by editing your POI files (idx,url) which exist in your navigation DVD or your USB depending on your hardware, the format is described at the beginning lines(check the following picture), they are easy plain ASCII files describing a table with fixed bytes as columns.
In order to add a new POI just take a look at those already exist in your files!
The headers are very long so they can not be fitted here but I have took a picture from one of them (url extensions).
The idx is similar to url, do not panic if you hit with some weird symbols. just copy them and it will work!
There is a complete description on Navteq geometrical(map) format here :
Sorry I did not find a free source, but it has a 30 days trail.
Do not mistake url files with internet shortcut, the url I am talking about is a plain ASCII file which includes POI info