i too was weary of running it at 5 v so I used 2 AA batteries for my tests, should be near the 3.3V.
my assumption is to set the slave address as
i2cslave $A4, i2cfast, i2cbyte
i'm not sure that 18x can handle the i2cfast communication but would think the nunchuck would adjust.
i'm very new at this and i'm not all that familiar with different variants of basic, not sure how to translate it to picaxe,
in the article, he does this to read from nunchuck using picbasic Pro
XX: 'read nunchuk
i2cwrite sda,scl,$A4,$40,[$00]
pause 10
i2cwrite sda,scl,$A4,[0]
pause 10
i2cread sda,scl,$A5,[a1,a2,a3,a4,a5,a6]
Best i can tell it would translate to PicAxe,
i2cslave $A4, i2cfast, i2cbyte
writei2c $40,(0)
pause 10
writei2c 0,(0)
pause 10
readi2c 0,(b1,b2,b3,b4,b5,b6)
unfortunately when i tried using this method all i would get is 255 in all 6 registers.
my experience with I2C is limited to interfacing with EEPROMS, most likely i'm doing something wrong.