Psalmcaster is on to a winner. Listen to the song, and just try to pick out the root note of each chord and go from there. Also, try a forum search on 'Diatonic Harmony' - I think that will help you.

Once you know what the chords are, you can use the Diatonic Harmony stuff to figure out which key the piece is in, and then you'll know what scale(s) would fit for lead / fills etc.

If the songs in question are well known, it might be that you can cheat a bit and find tab on the internet for them...