This is effing cool.
I am doing this with Garmin stuff here.

Latest free Google Earth version.

Download your track data from your GPS unit with MapSource.
Save it to disk.

Convert it on this page here to a format that Google Earth can use for
altitude data.........

http://www.gpsvisualizer.com/map?form=googleearth


A fellow over at sci.geo.satellite-nav explains just how easy it
is....

"Leave everything on the complicated form exactly how it is and the
only thing you have to enter is the UPLOAD field for where your *.GPX
file is on your hard drive. The web site converts it directly to a
*.KML file. Save it then click on it and your Google Earth starts up
and it is in true 3D mode to view the track of the plane."


In Google Earth right click on the track, select "properties"

Go to the alittude tab and select "absolute".


Have fun playing around with this.
I find that changing the elevation exageration under options helps see
things a little better too. 1.5 works nice.