need help with imagemagick resize scrip please.

my ISP has told me i need to use imagemagick to resize images but i cant get it to work. this is the only script i have tried that has partworked.

<?
// to convert
$command ="convert -resize 100x150 d:\nuvocreative\userimages\imgmagic\testbig.jpg";

exec("d:\nuvocreative\userimages\imgmagic\$command",$a,$b);

// Put a file called test.txt in the directory of this script

exec("copy package.xml package2.xml",$a,$b);

// If you now have test2.txt in the directory, then exec works fine
?>

the package.xml test part to see if exec works..

but the otherpart dosent the resizing part.

please help this is getting realy anoying thanks aron.