When I use this script with my employer's computer (Linux 2.0.36, Apache 1.3.9, PHP 3.0.12, OCI8 and Oracle):

for ($i=0; $i<10; $i += .5) {
        echo $i . "<br>";
        }

I get an infinite loop, because $i remains zero. If I increment $i with 1.5 each time, it gets actually incremented with 1, so it seems like the increment is floor()'ed before.
The script runs perfectly on my workstation (Linux 2.2.13, Apache 1.3.4, PHP3.0.7, MySQL).