HOW DO YOU LOAD MAPS TO THE GPS UNIT?

You need to install the map software on your PC. From there, using the map select tool, select the maps you want to add to your GS unit and then send them to the microSD card which will show up in the SEND window.

No you can just load the topo and have the etrex directed to the card that you have installed and deactivate the pre-installed map

In Map Setup page, scroll over to blue 'ball' icon (second from right), press lower left button on side of GPS unit, use Thumb switch to scroll down to "Show None", click Thumb switch in. All maps will disappear. Press lower left button on side of GPS unit again, scroll down to "Show Topo.....", click Thumb switch in. Your Topo maps should now show onscreen.

The reason your Topo map might not have shown is because, if you leave the Navigator map showing, and then just press "Show Topo", the layer showing Topo will still be under the Navigator map. This is why I always tell it to show none, and then load whatever map I need to see onto a bare screen.

If this solved your problem, please come back and rate our answer as this assists others. Thank you.

Your MicroSD card may be full just from the basic maps. Try larger card for additional maps. The vendors supply the minimum to keep the cost low and then force the customer to upgrade the resources at their own expense.

try this
https://www.youtube.com/watch?v=ex7fGF2sXqk

You need Garmin MapSource (Trip and Waypoint Manager) and a data cable. Then for free maps visit the murky internet sites and beware of what you download. I would not bother with a topo or marine maps on a grey screen GPS anyway as the colour maps will not be easily understood on a grey screen.

The preloaded maps are VERY generic, mostly major highways. They are not useful for geocaching.

The good news is that you can download free topo maps created by a very generous Canadian soul, Dale Atkin. The maps are free but donations are accepted. He is also working on US topo maps. I've used Ibycus and Garmin topo maps and prefer the Ibycus version.
If this solves your situation, please come back and rate our answer. Thankyou.

You can view segments of the maps at the Garmin site and it will show you how much detail there is.
Go to http://www8.garmin.com/cartography/mapSource/topous.jsp#
and on the far right side of the page, you'll see a link to Mapsource Map Viewer Topo USA 2008. Click on that and zoom in to your area.
Yes, you can download the map segments to your unit.

on my 60csx i go to main menu/setup/maps and select the items I want to display.
may be similar on the vista

You need to select all the segments at the same time and then transfer to the GPSr. Do not send one set, then another as the second set will overwrite the first set.