This isn't the only way, but it works for me.
1. Find the free charts pages at Astrodienst (
www.astro.com). If you are not a member, join. As a member, go the the "free charts" pages (you may have to scroll down to find the one with all of the different chart options.)
2. Input your birth data: date, location, and time. If you don't know your birth time, input it as "unknown." It's best, when you look at the various options, if you reduce the chart size to 75% so it all fits on the screen at a glance. On the type of chart you want, click on "natal chart and transits."
3. Left-click on your chart to remove all the extraneous info, then right-click on it to save it to your computer (you will see "save as" in the menu)
4. At the bottom of your next message, click on "Go Advanced" tthen on "Manage Attachments." Follow the browse/upload prompts to locate the image from you computer and attatch in to your next message. You should end up with a clickable thumbnail.
Do not simply paste your chart into your message-- it will expire. Do not try to link your image from your Astrodienst image on their site: it won't work. If you have another site where you can store images and link them for other people to read, a link might work.
There is also a sticky somewhere on this site with similar instructions.