If you want to build a multi-user gallery, use open-source is your best choice. However, if you are like me who need a fully customizeable gallery, you can handcode with some simple PHP script. I also use EXIF extraction code to faciliate visitors to have a quick view of my camera settings. See my website at the signature for example.
gallery.menalto.com would be your best bet. I'm using it on my own site. u can even integrate it with joomla/mambo. highly customizable. everythings all done for you. all you need is to upload the script and install it.