This worked for the Astro 220 Garmin, and should work for most other Garmins in Windows 7 installations.
Go to Garmin Support website and download to locate USB drivers. http://www8.garmin.com/support/download_details.jsp?id=591
This should take you to the USB software driver 2.3. Download and install it. This will update the Garmin drivers and add support for Windows7 64 bit.
This worked for our new WIndows 7 Fujitsu computer. It's not a DeLorme problem; it's a Windows7 problem.
I hope this works for you. If not, contact Garmin.