Actually, that's not true...There's a much simpler way than getting the sheet music and that's to simply look. That a look at the chords within a song. Quite often (not always, but quite often) the first chord is the the key...So, to test this, let's say you had a chord prgression of G C Em D (just the first thing which came to mind).
Now, write out all the notes in G,
i.e. G A B C D E F#, now because all of the chords can be found in this scale, G is the key...if the key doesn't come from the first note, then look again....after awhile you begin to see the chords within the scale, relationships on paper (e.g. the I IV V stuff)...
There's one way...keep reading through and just ask any questions if I've lost you...Good luck!

BTW - Failing all else, just ask! There's bound to be someone near by who knows!...(Show 'em the chords first though...)

[This message has been edited by Willdridge (edited 08-12-2000).]