If this process doesn't work for your 200, it shouldn't hurt anything. I create the IMG file with a $20 program called GPX2IMG. On my 750 the supplemental map just shows up automatically. If not, go through your menu settings on the Nuvi and look for "Map info" and see if you need to enter a check mark to activate the supplemental map. Once you have the file loaded and the GPS disconnected from your computer, when the GPS is back in normal mode instead of mass storage mode, see if you can find the colored lines of the tracks where you expect to.
If you already have a gmapsupp.img file in either place, feel free to rename it gmapsupp_OLD.img or the like first, then rename it back later if needed.
Connect your GPS to your computer, and load the gmapsupp.img file either into the unit's "Garmin" subdirectory or to your SD card's "Garmin" subdirectory. It'll be a transparent image file, with just the route highlighted in magenta. If you send me your email address via private message (click on my screen name, then "send private message to", I'll send you a "gmapsupp.img" file of the GPX file. I found all that out the hard way in the middle of forests in the mountains. And going off of an established road really blows its mind. You'd have to insert bunches of via points or waypoints on the route using Mapsource or Basecamp before loading it on the unit, to try to force it to recalculate it using the correct roads. Even if it did work with routes, Nuvis will murder an externally route created route anyway by recalculating it when it's loaded. Click to expand.OK, you have a unit there that won't work with tracks nor routes.