OK. I just upgraded my Garmin Etrex Legend ( the BLUE one!) to software version 3.90 just this minute (18:30, March 6, 2009) , so I will try and help you guys out if I can...OK? NOW...I use Windows XP Media Center Edition 2005 on a Dell Desk top.<<<<<This is important! The program you use determines which down load you need!
First, if you plug all your GPS and serial and USB cables in, look at the date and clock at the bottom of the screen on your GPS unit and see if it updates. If it does, your cables are OK. (May take a few minutes) (I use the SERIAL cable that came with the Etrex and a USB to RS232 link up made by ITech, part number GUC232AWM) The serial RS232/USB cable should be industry standard and all the same, but who knows? Set the GPS to "SETUP" then to "INTERFACE", this is so you can see what is going on inside it. Then go on the "SYSTEM" and scroll to the "Software version" and see what is there. If it is 3.90, it is already updated. Should also have your unit ID number on there. Write this number down.
Next, go to www.garmin.com and go to the "home" page. It helps at this time if your unit is registered and all that kind of stuff. Enter your unit model and serial number. I also registered my "Mapsource" topo maps and the version number etc. It also asks for the serial number of the map program. Now click on "support', then scroll down to "webupdate". Then click on the version of upgrade you want.
Ok. Now the tricky part...When you get to the part where it says "search for device" and you click on this and it says "no device found" don't despair! UNPLUG THE USB CABLE, then plug it back in! (That's all I did, and it took right off.) It should then download to your computer into a temp file, but upgrade that to a solid file, then feed it to your unit. Your GPS should have a grey screen that says "loader" in small letters, then "sofware loading" in small letters, and this should take about five minutes. When done, it will have the new software version number, write this down, and check to see the new stuff is in there.
Then, look at your computer program list for "GARMIN" and see if it leads to WEBUPDATE. If so you are all set to go.
If not, Well, I tried. Worked for me.