There are (I believe) a number of tutorials in the forum that discuss it, as well as sometimes providing pre-built navigation computer OS discs to load it from.

For modifying the maps, you can either do it yourself with software you can find discussed here, or you have have one of the commercial suppliers sell you a ready-to-go map disc. If you have a legitimately-purchased copy of the current year's maps, then that may stand as an affirmative defense if BMW or TeleAtlas ever decided to sue you for pirating their property (the maps), since you already own the genuine article.

A web post or query for maps with POIs added, etc. in one of the more frontier-like areas of the Internet may get you contact information for someone who can supply you with an out-of-the-box plug-and-play solution, along with references from users here who can agree or deny the accuracy and quality of the info, as well as how the user interface design works.

There should be at least pointers here to some of it. In a cursory glance, I note two projects hosted here - POISoN, and Pimp My Nav.

Commercial projects telling people how to copy "borrowed" maps to produce complete map discs aren't very welcome here. Nor are sellers on places like eBay who say that they have 100%-legit discs with speed traps, speed cameras, etc. all prepared on the map disc. for your simple exchange of cash for map discs. The discs you get back may have been modified in some other way which might not matter, except that a panic-mode "Where's the nearest Police Station" could redirect you to the closese state Fish & Game Warden station. If you decide to purchase a packaged system from one of those guys, I'd ask if they were using genuine BMW/TeleAtlas discs (and from what year), and how the can be reached in the event you aren't satisfied with the product abd wish to return the item.

That's one of the reasons that there are some DIY products available - they assume you already bought the real map discs, possibly support the running of this forum, etc. And the people who wrote those tools are often here to provide help to newcomers.

The companies selling pre-modified maps are trying to grab a lot of cash in a short time and then vanish. I have no experience with them, but one company is selling the software update disc (only needs to be run once) along with both the east coast and west coast map DVDs for $49.99. At that price, there's no valid sublicense of the $199.99 map data between TeleAtlas and you, which is why I suggest buying the real maps, either at a BMW dealer (possible parts discount, possibly sales tax) or from TeleAtlas directly ($199.99, no discount, possibly sales tax) amd then making backup copies of these discs and experiment on the copies.

I had a good deal more to say, but the sleeping pills make me look like a chimp at a typewriter, and the quality of the chimp's writing is above mine.