Thx for all the details.
I will try to be clearer - trying not to get lost when offroading in the desert is the ultimate goal.
I can work with that. That's the great thing about my GPSs ... even when I'm totally lost I always know exactly where I am.
Do you have to "build" the trail before - downloading individual coordinates and then following them once you are off-road?
Well, that depends... Does the trail show up on a topo map that you can load onto, say, the Nuvi? If so, then it would seem to me that the point is to simply follow the trail using your eyes, on the trail and on the GPS screen. That's the simple method.
Obviously you need to add track recording to that so you can visually follow the track backwards when it's time to go back.
Or are you looking for guidance instructions from the navigation program, similar to what you would get with on-road routes? That's a whole different kettle of fish. With Mapsource/nroute you could do that but you still need to be able to see the trail on the topo map in Mapsource. You could use the Route tool and click on key points on the trail to get a "route" that could be used by nroute to provide directions. I've used this method in Mapsource to measure the distance (eg. length) of a trail I plan to ride. But I'm not sure what value this would be. .... Well, if you activate the route it will lay a heavier, possibly much more visible, line over the trail lines on the topo map. That might be helpful.
In any case, you can play with this in Mapsource. Just select the desired topo in dropdown map list, click on the Route tool on the toolbar (or TOOLS > ROUTE) and start clicking along a trail. For guesstimating distance I click at every change of direction so I get a series of straight lines that are somewhat close to the line of the trail. When you are done with the "route", just right-click on an open area of the map screen and click on "cancel". Now you will see the "route" displayed in bright yellow (I think that's the default, or maybe it's bright purple). If it's not displaying onscreen you might need to click on the Routes tab, right-click the route you just created and click "Show selected route on map".
If that's not what you are looking for, a little more description would help zero in.
If the trail(s) you want to follow aren't on the maps at all, then I have no idea how you would do anything in advance. All I can see is that you need to be able to record a track as you drive the trail so that when you turn around to go back you can display it onscreen and follow it back.
If I'm making this way more complicated than it needs to be, just holler. Perhaps it's as simple as setting a waypoint (Favorite, whatever) at the point where you jump off the road and being able to tell the navigation device/program to take you back there using the "offroad" route preference setting. That would put a straight line "route" from where you are back to the jumping-off spot. Each time you come to a fork in the trail you can make sure you turn so you keep headed in the right direction. That should even work with the Nuvi.
Sometimes simple is good enough, and Good Enough is almost always cheaper.
So starting from scratch: a) netbook+ b) receiver+ c) software.
From what I understand: netbook is fine, receiver to be obtained (but potentially predicated on the type of software)
It looks like the choices are the killer!
Ah, but it's great to have choices!!
Play with Mapsource and imagine that you can simply add navigation features to it that will use whatever you can create (or download nroute
.. it doesn't need a receiver to see the added navigation features and play with the tools to see if you can get something useful onscreen) and see if that's getting us closer to what you need. Then we can move forward from there, or follow some other option altogether, depending on what you find.
If you decide to play with nroute, check out the Tracks tab to see the options. Look over to the right side to see the Track options and more under the Active Track Filter. If you want to see what an existing track looks like in nroute or Mapsource, just let me know and I'll attach a couple to a message for you to play with.
.... Ooops, I completely forgot that sometimes you can find track files on the internet for a place you want to go. That's how I found some interesting trails out in the Rockies for my mountain bike last month. Other people had already ridden there, recorded their track files and uploaded them to share for others planning to ride or hike the same trails.
I'm not trying to sell you on Mapsource/nroute, or even a Garmin solution. I just happen to know them pretty well and you already have Mapsource and there are lots of Garmin-compatible topo maps available, commercially and in the wild. This will help us move towards something that might work for you, even if it's just pointing out details of why it's not working.