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There are a number of tools that will automatically generate image map code for you, a search in your favourite search engine for something like "image map creation tool" will point you towards them. For example, Dreamweaver comes with a built in one.
As for optimising the download time of image maps, this is more or less dependent on the size of your image, and the same principles apply as optimising any web image.
If you are thinking of using a particularly large image (dimension wise), it may be worth considering splitting the image into a number of smaller images.
HTH