The KJV does not teach that preaching is foolish. The use of the word "foolish(ness)" here found in its context clears up the confusion.
In verse 18 we read that the "preaching of the cross is to them that perish foolishness." The text isn't saying that it's actually foolishness, but that it is perceived to be this way by certain individuals.
Verse 23 further builds this context by pointing out that the Gospel is "foolishness" to the Greeks, and a stumbling block to the Jews. Again, it's not (in its essense) foolishness (for it's the power of God according to v.18), but instead it's perceived to be foolishness by certain individuals.
Verse 24 tells us further that it is the power of God, and the wisdom of God. And verse 25 states that the foolishness of God is wiser than men, and that the weakness of God is stronger than men. It should be obvious that the author is not actually suggesting his God to have foolishness and weakness, but instead he is making an argument that we ought not look to what man considers wise and strong, since the power of God itself is misidentified by these individuals to be foolishness.
The conclusion is not that preaching is foolish, but that it's perceived to be this way by certain individuals. The NIV states that the message is foolishness, but the same exaplanation stands. The author isn't categorizing the "message of the cross" and "preaching" with foolishness. He's merely using the term loosely.