nikon L100?

In iPhoto, go to the iPhoto menu and select Preferences.
Click General.
In the "Connecting Camera Opens:" drop down, select "iPhoto.

Cheers!

Now within iPhoto you should see a section on the left titled "Devices". Your camera should be there. Highlight it and you will see an Import button in the lower right.

I assume the camera is on, right? More than likely it needs to be in display mode, not taking pictures mode.

Is it connected via USB, or Firewire?

Quit iPhoto.
With the camera connected, an ON, launch the Image Capture application (found in your Applications folder). the camera should at least show up there on the left.

Take a look down at the lower left corner of the Image Capture window, do you see a tiny square button. Click it and a pane will open with the option "Connecting this camera opens...". Select iPhoto from the drop-down menu.

Then quit Image Capture and relaunch iPhoto. Does it appear now under Devices?