Generating files in Microsoft PowerPoint and exporting them to EPS is very useful. A really good site for this (with pictures and everything) can be found here. I also put some notes below that worked for me (in addition to using the directions found on the site above), but I cannot guarantee that they will work on other versions of PowerPoint. So good luck.

1. Create a custom size page large enough to fit your drawing (using "File->Page Setup..."). In my experience PowerPoint put bounds on the smallest and largest figures I could export. For example, PowerPoint will not let you (to my knowledge) export anything of width less than 3.66 or height less than 7.5. If you want a figure that is smaller (say width = 1.8 and height = 2.5) create and draw the figure at that size. Then go to "File->Page Setup..." and scale both the width and the height by the same amount to fall with in the valid range (to 5.4 and 7.5). The figure will automatically scale with the page size.
2. Draw your figure.
3. Follow the instructions here.