Well, you could split() the string into an array and then join the first
200 parts together (using join() or string concatenation).
But the, the way I'd suggest is to use substr():
http://www.phpbuilder.com/manual/function.substr.php
$first_words = substr( $full_text, 0, 1000 );
Now, substr() works on the number of characters and not the number of words, but since words can be different lengths, it may make more sense to display the first 1000 characters (assuming approx 5 char per word to give you approx the first 200 words) than to display the first 200 words. If $full_text contains a lot of long words, hyphenated words, ellipses without spaces, etc, then you could have a very long 200 words.
I find it easier to design a text field around the number of characters rather than the number of words.
Just a thought and I hope this helps...
-Rich