OK, now I want to draw some chemical models and post them. I save them as a jpg file and upload them to imageshack and the reference them there?
Exactly. After uploading them to ImageShack, it'll even provide you with easy cut-and-paste samples of "code" you can use in various contexts to present the image. Use the "Hotlink for Websites" ones, it's appropriate for HTML venues such as FreeRepublic. There are a couple of "Hotlink for Forums" types, but FreeRepublic won't recognize those, they're for online forums that use a different kind of linking syntax.