i first learned this using the RE-RX7. if you are using a steering wheel, this will be really easy. since jgtc cars have plenty of grip at default settings, it is good to start out with it. to drift using the oh-ch1t button, you need to find your optimal speed. in trial mountain for example, there's sort of an s-curve after the long long left corner (going normal, not reverse). you really need to control your speed there for the oh-ch1t button. now for using it. attain the right speed(this will adapt after a couple of laps), let go of the gas and hold the O (hence, oh-ch1t) button and slightly turn your wheel to the direction for which you want to go. do not attempt to step on the gas when you are pressing O. that will just create oversteer. once you feel it sliding, counter-steer. on 900 degree steering wheels, you need to turn about 45-90 degrees, depending on your speed entry(you'll later go beyond 90 for high angles). as soon as the car starts to grip back in motion, floor the gas so you get wheel spin so you can still slide. determining when the car will slightly begin to grip back takes awhile to get used to. sometimes you end up gripping and flying towards the other way due to counter-steer, or if you do it too early you'll spin out like how anyone would.
if you strictly play tsukuba, the very long right corner (in normal direction) is complex. i've played both 4wd and FR using all of the r32s as an example, and both are very difficult in this corner. it requires using the O button several times during the sequence of sliding. i normally slide into the corner to get some angle to start out, and then, before the car starts to get back into a straight position, i have to time the use of my e-brake and how long i'm suppose to use it. this corner feels like the real deal. i go drifting at Willow Springs in California with my real car, so i'm a little used to the "new" physics in gt4. i wont get into that though since it's sort of silly to bring it up anyways. it takes time for me to sink in what to do and where, but it's getting there.
one thing i have to note though is not to turn your 900 degree wheel to full lock. that will just whiplash you as mentioned earlier. once you have A LOT of speed and control, which is rare in tsukuba and trial mountain, full lock will be necessary for the high angle drifts. the only places where i think full lock is actually usable is on that long corner in tsukuba and in trial mountain left turn before the left turn entering the bridge. since you can blast your way in, you'll have so much speed. i will post a video sometime. my pvr lags though...
to the above poster, u look guudd. s2k's rock. i want to buy one soon (a real one) but drifto take all of my $ away ='(
