how do I download video to i-movie 5.0 using my Canon SX-40 camera

Should just be able to plug camera into computer. It will prompt you if you would like to Save files onto computer. Click the files you want and ice that is done you can do some simple drag and dropping or adding files trough help tabs in iMovie

As long as you can download images to the computer and the images are in a format compatible with i-Movie then you can use iPhoto and iMovie. Note these are two different applications that do different things. iMovie, however, is Apple software and many manufacturers don't go out of their way to make things compatible with Macs. I have a Canon camera (lower range model) and it only produce AVI format movies which is an old Windows format. I've never used iMovie but I somehow doubt it would open my AVI.

The software that comes with the camera does a lot of basic things. You can also read the user's guide and software manual at this link I do note in one of the manuals there was mention of a preferred shooting mode for Apple with iFrame format. Read more about that at http://en.wikipedia.org/wiki/IFrame_%28video_format%29 where it menions iMovie compatibility but only iMovie 9.

You might want to learn a bit moe about the modes produced by your camera then perhaps ask your questions on the iMovie forum (and hope there are some users of older iMovie and they don't just all go and tell you to buy the newest).