I've seen pics of his lights on the Mercs boards...and he doesn't need any resistors. Just 2 9v batteries wired in series with the lights should work fine.
Most LED's require a 10k ohm resistor in series with the battery to keep from burning out. I believe the color code is Brown Black Orange Gold.
Best way to remember your color codes is with this saying.
Bad = Black (0)
Boys = Brown (1)
Realize = Red (2)
Our = Orange (3)
Young = Yellow (4)
Girls = Green (5)
Become = Blue (6)
Very = Violet (7)
Good = Grey (8)
Wives = White (9)
So a 10k ohm resistor would have: Brown (1) Black (0) Orange (+3 zeros) and the gold is the tolerance value.
Now you can do the math yourself before you get to the store, and go directly to what you need. Your lucky if you can find someone in Radioshack that knows this in the US. =)