imagettfbbox returning screwy values

I'm having this really bizarre problem with imagettfbbox. The values it is
returning seem to be way off the scale. I have gd and ttf support compiled
into php, (running on latest stable apache 1, gentoo linux, latest stable
php)

When I call imagettfbbox I get very very large numbers back. They don't seem
to make any sense at all.

Here's my code:

<?php

$txtSize = imagettfbbox ( 30 , 0 ,
"/usr/X11R6/lib/X11/fonts/truetype/georgia.ttf" , "test" ) ;
print_r ( $txtSize ) ;

?>

And here's the output:

Array ( [0] => 1076630208 [1] => 137911840 [2] => -1073777096 [3] =>
1073930763 [4] => 1076630224 [5] => 1076625940 [6] => -1073777064 [7] =>
1075882071 )

Has anyone seen something like this before? Suggestions? It's not a dodgy
font. Switching fonts makes the numbers change but only slightly.

For reference, my phpinfo is here: http://www.sympages.com/info.php

Help!

Thanks,
Simon