You can interchange UTM and DMS (or dd mm.mmm) and
have the waypoint point to the exact same spot.  The
easiest
thing to do is use the download from Snaptek and
download that into your GPSr.  Whatever program you
use will know how to tell the GPSr what the format is
so it will be loaded correctly.  Then just change your
GPSr to whatever coordinate system you want to use on
the trail (UTM or DMS).  The GPSr will correctly
convert it to display the new coordinates.  

However, you can NOT arbitrarily interchange Datums
(WGS84 and NAD27).  If you use the wrong one, you will
be about 200 feet off here in AZ.  If you make sure
that the download from Snaptek is loaded into your
GPSr using WGS84, the locations will be correct.  THEN
you can switch your GPSr to NAD27 to match your paper
topo maps and the GPSr will convert the waypoints to
the new datum.  Also, if you enter waypoints from a
paper topo map, make sure the datum is set to NAD27.

You can do what you want to do, you just have to make
sure you do it correctly.

If you look at the bottom left corner of the topo map,
you will see text mentioning the difference between
these two datums.  There will also be a small black
plus sign showing the new "corner" of the map if it
were to be redrawn using WGS84.  

Bob


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