If you can make up data, you can do it in excel. If not, then I'd be tempted to draw it in powerpoint. I've used other packages, such as CorelDraw
I did the following by making the basic plot in excel, and added some of the lines and the text in powerpoint. Depends on what you want to do. I don't personally like the way excel makes plots, so I usually load my data into MatLab. But that would be a little more difficult than what I think you want to do.
edit. crap, that's tiny. If you can tell if that's sort of what you're looking for, then you've got good eyesight.