rubble express,
The Colorado is a great unit. You can also look around the Geocaching web site and pick up some resources that you can use with your Colorado and your StreetPilot 2720. Check out Geocaching Home Page for the Geocaching Resources and go to Tools and Downloads, this includes some great utlities including "Geocaching Swiss Army Knife (GSAK)".
Which etrex do you have, I have used an etrex legend for several years as well as the Garmin 60csx. I enter the coordinates manually on the etrex by going to the main menu and using the mark feature, once I put in a waypoint I edit it to the coordinates I want. This is kind of a hard way to enter information but I have used this unit so long that I can do it quickly.
I use my Nuvi 350 to get me close to the coordinates. Some caches are in locations that do not have a direct way to get to them, the 350 gives me good directions to the area.
This may also be a help to you. It is a site that 8.1al had posted a while back
http://pilotsnipes.googlepages.com/index.html