professorhat:Assuming you're using Windows, it will be presented as a new hard drive in My Computer e.g. if your current hard drive is called C: and you maybe have a CD/DVD drive called D:, then this new one will be called E:
This is how my Western Digital USB hard drive works. When I plug it in it automatically switches on and calls itself E. I have a short cut to it on my desktop.
professorhat:If you want to move your iPhoto and iTunes files to it, you'll need to to do some re-jigging. Do a search on Google for "moving itunes library to external hard drive" and you'll find numerous articles and even videos to help you do it.
I have to this a lot because the hard drive on my PC is only 50gb and about 20 of that is taken up with stuff. So for phots and music I have them in folders and drag and drop between the the external drive and My Music and My Pictures. Drag and drop works quickly , leaves a copy and I have not had any issues. So when you get a new hard drive make a folder in it called itunes and then drag and drop all your music files into it. I do it in batches of about 5 files at a time. I only move the music files there, itnes remains on the computer. I then go into itunes and tell it where to locate the music on the hard drive. Do the same for pictures and anything else.