Image upload dimension vs. quality

[tentim]

I want to have users of a site upload their pictures
to a database which will then be displayed in a profile
template,i'm using a fixed dimension in the template.
Since I have no control over the dimension of pictures
from users,I'm afraid the quality of the displayed pictures
will be affected by forcing them all to a fixed dimension.
Is there any way to fix this with the php upload script
or some other way to handle this.
Thanks.

[Ernie1]

 $uploadedfile = $_FILES['userfile']['tmp_name'];
 $src = imagecreatefromjpeg($uploadedfile);
 list($width, $height) = getimagesize($uploadedfile);
 $newwidth = 100;
 $newheight = ($height / $width) * 100;
 $tmp = imagecreatetruecolor($newwidth, $newheight);
 imagecopyresampled($tmp, $src, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
 $img = "images/" . $_FILES['userfile']['name'];
 $t = 1;
 while(file_exists($img)){
     $img = "images/" . $_FILES['userfile']['name'];
     $img = substr($img, 0, strpos($img, ".")) . "-$t" . strstr($img, ".");
     $t++;
     }
 imagejpeg($tmp, $img, 100);
//insert into table set image_path='$img'...