While the Garmin eTrex Vista HCx is a pretty neat device, the track logging really sucks and it his hard to understand what the device does when it records your track. Here is some information I found while skimming through the web on finding some answers reagarding the track logging.
You get to the Track menu either thru the Main Menu (press the Menu button on the lower left side of the Vista twice) or by cycling thru the main pages by pressing the Quit button (upper right button). Be reminded that the Track menu is not listed in the main menu if you included it to the pages being cycled by the Quit button!
Activating logging to the SD-Card
By default the Vista HCx logs to the internal memory. If a SD-Card is present in the device you can activate additional logging to the the SD-Card - as well to the SD-Card's memory.
Saving the active log
This saves the active tracklog to the internal memory, not the card. In addition to stripping out the timestamp information, it also reduces the number of points in the tracklog to a maximum of 500.