ok, heres what you do
lets say that from a2:a1000 is th column you have will all these different names
in b2 type
=IF(A2<>0,
COUNTIF($A$2:A2,"="&A2),0)
it's on 2 separate line because yahoo wouldn't display it all but the countif part should be right after the "," in the first part
after you enter that formula, copy b2 and paste down to b1000. what this does is it looks at a2 and counts how many times the value of a2 is found above it. so this obliously will be 1, lets say the the next name is different than the first one, it will also be listed as 1 because the first one is different. if the third one = the first name or the second name, it would then be 2 because it is the second time that name occured, and so on and so on. now select column a, go to format > conditional format, click on formula is and type =if(b1>1,1,0) and then click on the format button, click patterns tab and change the color to blue or whatever color you want it to show when there is a duplicate. hope this helps.
feel free to e-mail me with questions.