Title - 'Easiest way to drag internet images into iphoto?', are we to assume you are selecting and dragging a web page image?; or, are these images saved on the Mac, and 'iPhoto' will not accept them when dragged onto it ('Applications' folder) or on the 'Dock'?
The solutions provided below will be based on the assumption you are trying to drag a web page image onto 'iPhoto'.
Your post is very vague, you did not supply:
The MacOS X version installed.
The name and version number of the web browser(s) you are using.
The version number of 'iPhoto'.
'i'm having difficulty doing this one. it seems simple dragging an image into my iphoto icon... but i can't get it to work.', no - it does not work. You cannot drag a web browser's web page graphic onto 'iPhoto', in the 'Applications' folder; but, you can drag the web page image onto the 'iPhoto' icon on the 'Dock', and it will be properly imported ... so long as if you have 'Tiger' (10.4.x) installed. 'Panther' does not offer this capability.
(iPenguin) - 'In Tiger, with Safari 2.0 (and maybe even earlier, but I don't think so...) you can just control click the image and select "Add Image to iPhoto Library', 'Safari' v. 2.x, with 'Tiger' - yes; v. 1.2.2, with 'Panther' - no.
Most web browser's allows one, via a contextual menu, to save / download an image to either a specific folder or a folder of the user's choice.
Then there is the tried and true way. Click on the web browser's graphic image and drag it to the 'Desktop' or any opened folder.
Any image(s) in a folder, or the folder of images, can be dragged onto the 'iPhoto' application's icon or 'iPhoto' icon on the 'Dock'.