Trying to install WordPress

Check to make sure you do not have any spaces before <?php or after your ?> tags in the php file you are trying to access.

No.
And if you read it more carefully it even tells you exactly where the problem is: which file, which line.

And for some reading: http://wordpress.org/search/Warning%3A+Cannot+modify+header+information+-+headers+already+sent+by?forums=1
over 700 hits…

http://codex.wordpress.org/Answers-Troubleshooting#Headers_already_sent
See the interpreting the error message, which has also been referred to zillion times.
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