Using a Mac mini as external/storage hard drive

I am about to take delivery of a new iMac, which I intend to use as an 'everyday' computer and mostly for photo processing .

I have a large iPhoto library already that I would like to 'archive' but also be able to access easily.

As I have also inherited a 4GB Mac mini , which I have connected to a second monitor, could I make use of this as a storage for this photo library (as well as a 'fall-back' computer for everyday use?

If so, how do I transfer the photo library from my outgoing computer to the mini - via another hard drive, dragging, dropping and then opening up again? Or what?

You can guess from my use of language that I am not terribly computer-literate, but all advice gratefully received!