PHP text replacment help

Yes, there are several plugins that do that.

http://www.coffee2code.com/archives/2005/03/29/plugin-dynamic-text-replace/#more-43
is one.. c2c might have another there.

I use phpGiggle. It spots key words and replaces them with the word as a link. Using your example, if Google is your phpGiggle word and you have it set up to point to http://www.google.com, then all you have to do is type Google in your entry and phpGiggle does the rest. I have over 150 words in my phpGiggle list and it doesn’t slow down the site. You can download it at:
http://sourceforge.net/project/showfiles.php?group_id=102748