Warning: exec(): Unable to fork

Hi, I curretly running: PHP 4.3.4 on a windows XP with IIS, This is the first time developed using a windows platform (normally I use apache on linux), but I'm trying to run ImageMagick in the background to resize an image, as a test I'm trying to run the cmd shell, using exec (I've tried system, exec, passthru), yet they all give this error: Warning: exec(): Unable to fork [C:\WINNT\SYSTEM32\CMD.EXE /?] in index.php on line 45 From googleing this would seem a windows specfic problem, but as of yet I have not found an answer, it seems pretty common on windows. Has anyone else managed to get around this yet? or can advise on what the error could be due to? Thanks Mark