Help with image resizing!!!

[Designer_101]

Hi
I'v hit a glitch in my bebo, myspace, facebook ect style website.

I basicly need help with a script to resize an image, of which directory is stored in my database.

<div id="profile" class="<?php echo $user_data[skin]; ?>">
<img src="<?php echo $user_data[dp]; ?>">
</div>

Bering in mind i cant have the image just simple resized to a fixed point because some images will "megapixelized".
I'v searched all over the net for help but cant seem to find one i understand.

All Help greatly appreciated.
Thanks