If you're having trouble breaking loose, I can only sugget you shake the car slightly at the end of the braking and try to jerk the back of the car out of line.
If that doesn't work, you could always do insane overkill: Get slightly tail-out in the wrong direction before braking, modulate your braking and your countersteering to keep a constant angle (as high as you can control), let off of the brakes, let the rears regain traction and change the car's direction, and bingo, you're drifting. I used this on a stock S15 for Tsukuba's hairpin, and it looks bloody mad to watch in a replay. The image is still very vivid, despite it being 6 months ago.
The 'slight shake' I decribed is what I now use for wheel, because that's all that's needed to get the tail out when using a steering wheel. If you're using DS2 and not using any very clever settings, the rediculously complicated technique is your only option (but don't despair; it's odd, but flippin' sweet!) if you want a drift througout the entire turn.
And if it's maintaining drift you're having trouble with, you just need to remember one thing about GT4's physics: You can't do donuts. By which I mean, excessive wheelspin in a RWD car has a negative effect on momentum and doesn't induce much oversteer at all. You just need to smoothly modulate your throttle on the very edge of the rear tires' capability.