The document comparison features in Word 2003 are extremely poor, and often results in the user removing parts of documents they did not want too
The only rational choice is to use other software. There are a multitude of text comparing software in the marketplace, but to do this within Word, the simplest answer is to upgrade to Word 2007 or later versions
From Word version 2007 the ribbon command "Review" and "Compare" are easy to find, and operate reasonably obviously. And they have a nice clear layout of merged changes, and the before and after docs
The small cost of the upgrade will be well worth considering the time you will waste in 2003 compare, and the potential damage to your documents it could cause
Any suggestions by others that you can use the compare features in 2003 is mischievous, and has not well thought through given the long term consequences of parts of your documents being silently deleted