In reply to King Arthur:
I am afraid Garmin software support often leaves a lot to be desired
For example, the WebUpdater states compatibility from Win XP SP3 (older than yours!) upwards:
https://www8.garmin.com/support/download_details.jsp?id=931
But the different, specific FW updater for your GPS unit requires Windows 7 (newer than yours!), as stated here:
https://www8.garmin.com/support/download_details.jsp?id=3709
Both seem to be superseded by the website version (my.garmin.com), which I have no idea how it works. Which one should you use - I have no idea... (and there is no list of the devices the WebUpdater supports either). I am almost afraid even the support at Garmin have no clue at all!
What is the FW version of the unit (usually shown after startup, or somewhere in the system submenu)? The second link shows 3.20 (from 2009) as the latest firmware, although there could of course be an even newer one via the WebUpdater...
What's worse, Windows Vista was probably the second worst (in terms of compatibility, drivers and so forth) Windows just after 98 (or the other way around). So even if the first link shows compatibility, actually it might be quite different...
I would really try updating via a newer computer if I were you.
Good luck
Post edited at 19:37