Thanks to Brice Delage delage.brice@wanadoo.fr:

Billy uses standard tuning live exept for Just got Paid,  open E :
E/B/E/G#/B/E

On previous tours, he used other tunings.
    -Rhythmeen : C/F/Bb/Eb/G/C (standard, but 2 tones lower)
    -Bang Bang : B/E/A/D/F#/B (standard, but 2 1/2 tones lower)
    -One of necks the 2 necks guitar for "lowdown in the streets" (check
rockpalast DVD) is open C : G/C/G/C/E/G (your need to put light strings,
otherwise "TZOING !")
    -The live version of "Nasty dogs" on the "What's up..." Maxi is :
A/D/G/C/E/A (standard, but 3 1/2 lower)
    -On the 2004 Tour, he used a D/G/C/F/A/D for the song "Goin' down"
(standard but one tone lower).

In the studio, he uses a lot of tunings.
On mescalero :
-Mescalero : Standard but 1 tone down (song sound G but he plays in A)
-Two ways to play : Standard but 1 tone down (song sound D but he plays in
E)
-Alleygator : Open C (not the same as "lowdown in the streets") :
C/G/C/E/G/C
-Buck nekkid : Standard but 1 tone down (song sound G but he plays in A),
solo in open D : D/A/D/F#/A/D, but live he plays in G with standard tuning
(check it, the riff is slightly different)
-Goin so good : Rhythm : Same as "rhythmeen", lead : standard
-Me so stupid : Same as "Rhythmeen"
-Piece : Standard
-punkass boyfriend : Standard
-stackin' paper : Standard but 1  tone down (song sound F# but he plays in
A)
-what would you do : rhythm : same as the live version of "nasty dogs", solo
: standard, slide gt : certainly open E
-what it is kid : Standard but 1 tone down (song sound D but he plays in E)
-Que lastima : Standard but 3 tones down (song sound Eb but he plays in A)
-tramp : same as "rhythmeen"
-Crunchy : Standard but 1 tone down (song sound D but he plays in E)
-Liquor : Standard but 1 tone down (song sound G but he plays in A)