Thanks Steve for the direction!
For the record, this is how I did it (in .htaccess):
# Redirect old About Us-Services URL
RewriteCond %{REQUEST_URI} ^/help.php$
RewriteCond %{QUERY_STRING} ^section=about$
RewriteRule ^(.*)$
http://services.maperformance.com [R=301,L]
Unfortunately I couldn't include the hash on the original URL, since that is used for commenting in .htaccess.