From GpsWiki
Trail Maps
Create your own trail maps by using your PN-40 and Topo USA. How do I do it you ask? Well it is pretty easy following the steps below. The example used is from a mountain bike ride.
Get Data
First you have to have some data, such as a track, to make your own trail maps. Using your PN-40, make sure that you have your Tracks on and settings to how you want them here. After you are done hiking, biking or whatever you were doing, save your Track (this should ensure that you don't lose your data - this Track was renamed to 'mntbikeride'.
Exchange Data to Topo USA
Turn your PN-40 on and plug it in to your PC and hit Data Exchange when prompted to. From Topo USA, select the Exchange Button on the top tool bar or where ever you see the Exchange Button 
This will open up the Exchange Box.
From the right side of the Exchange Box, expand the Tracks by hitting the + symbol, this will list the tracks you have saved. Highlight the Track you want to Exchange and then hit the Receive Button.
After you hit the Receive Button, the Track will have transferred over to Topo USA and the name of your Track will be in the Left window of the Exchange Box. Hit the Done Button.
In Topo USA the Track Name will be listed under the Map Files Tab.
Track Properties
Next, hit the Draw Tab and then the Select Arrow 
and click on the Track. This will bring up the Properties Box where you can select the Color, Thickness and Style of your Track. When you are finished, hit the Done Button.
Then hit the File Button.
Copy the Track to a Draw Layer
Then hit the Copy Button
Then select Draw.
This will Copy the Track to a Draw Layer, you will see both the Track and the new Draw Layer.
Unselect the Track so just the Draw Layer is showing.
Cut Your Map
Select the Handheld Export Tab.
Select your Grids so that the data you want in your Draw Layer is totally covered.
Choose your Options. Make sure that just Draw Layers is selected.
Name and then Save your Map. After your map has been 'cut' it will tell you what type of Data is saved and how large the map is.
Exchange Map to the PN-40
After your Map has been saved, you need to Exchange it to your PN-40. From still within the Handheld Export Tab, hit the Exchange Button. This will bring up the Exchange Box again. Expand your 'Saved Map Packages' by hitting the + symbol.
Scroll down to your newly saved Map Package, highlight it and hit the Send Button (this will default the map being sent to Internal memory unless you specify otherwise).
DONE!!
Well that was the quick and dirty of it. While it may seem that there are a lot of steps, once you do it a couple of times, it is simple and easy. Here are the resulting screenshots.
Once you master the art of making your own trail maps, you can do entire trail network!
