From:
The Dictionary of Misinformation

A Little Knowledge is a Dangerous Thing:
This is not what Alexander Pope actually said, though many think it is. Here, from part 2 of his famous An Essay on Criticism, published in 1711 though written somewhat earlier, when Pope was just twenty-one, are the lines containing his famous, if often misquoted, phrase.

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There shallow draughts intoxicate the brain,
And drinking largely sobers us again.

The Dictionary of Misinformation by Tom Burnam, ©1975, Harper & Row, Publishers, Inc., ISBN 0-06-091315-0 (pbk.), Letter A -- page 5

Cheers
Dan (an interesting little book)