[PHP] Any good gif/jpg processing tool for PHP??

[Diego Fulgueira Pastor]

I am sure many of you have had this same problem. I want all uploaded images
to my site (gifs and jpg)  to be resized "on the fly" so that all have the
same width and height. Does anyone knows about a tool (free, if possible)
that can do this under Win2k, IIS 5.0 and that can be used with PHP 4.0?  A
php extension (dll) would be great. If it works only for one format (gif or
jpg) is fine.
Thanks in advance for any tip.

Cheers, Diego.