Can I use any MicroSD Card in my Garmin etrex Legend HCx?

I tried to insatll a osm map on my Garmin.
I did not work. I read all the stuff here and think I am doing it all right.
However I am not getting it to work.

The SD card I try to use was in my Nokia phone. I formated it, so it should be fine for any other purpose.

Two Questions:

- Is any SD micro card fine for the Garmin etrex Legend HCx?
- I have got a European Map from Garmin on SD-card. Within the <Garmin> Folder there is another file: GMAPSUPP.UNL. Whats that?

Thanks for your help.