a different slant on the problem would be to give the zodiac sign given a specific date.
This is do-able, you just have a list of dates and compare the user input -
CODE
semi-pseudo-code: figures/syntax not exact.
// grab user input
$date = $_POST['date'] // input could be '10 October 2005'
// convert $date to a timestamp
$timestamp = strtotime($date) // input now timestamp - '???????????????'
// dates for zodiac are pretty much always the same so just need day number
$day_of_year = strftime( %j , $timestamp ) // give integer 1-366.
// Now we can compare to an array - i'm guessing these dates and signs!
if (22 > $day_of_year >= 1) $zodiac = "capricorn"
elseif (166 > $day_of_year >= 197) $zodiac = "leo"
elseif (275 > $day_of_year >= 305) $zodia = "scorpio"
.
.
.
elseif (356 > $day_of_year >= 366) $zodiac = "capricorn
etc
echo "Your zodiac sign is: " . $zodiac
This is just an example - search php.net for the proper syntax of the functions and the correct dates etc.