jemtec, many software charting packages eg EzyChart have...

jemtec, many software charting packages eg EzyChart have automatic support/resistance buttons which do exactly as you suggest. Personally I prefer to put the lines in manually (by selecting a horizontal line placed with your cursor) because, in this case, I think the eye does better than the program. Perhaps though, this just means that the automatic program doesn't work well enough...
AnnaP