In the Photo Sharing and Critique members are able to choose a size (within limits) which they prefer for their shots. The gallery will automatically resize if the file is too large. Resizing is really quite a simple process and you can view a tutorial on how to resize
here. Hope that helps and by the way......welcome to Pixalo
PS if you have a look in the
Links and Downloads Section you will find a Photoshop action that will automate it for you.