Recently Garmin introduced the Communicator Plugin software
and Geocaching.com uses this to allow you to download geocaches directly from your web browser to a Garmin GPS. At present Geocaching.com restricts to one cache at a time.
Garmin has introduced Go Geocaching
on it's website which allows you to search for caches using a GoogleMaps interface and download multiple caches at once.
You can start here at a site Garmin has created that allows you to search thousands of geocaches and load them directly to your Garmin device. You must create a myGarmin account to use this feature.
Just tried this out and it worked fine with my 76C over a USB connection. It also included any additional (child) waypoints in the download.