If you have MS Office, Outlook will send it without an image in the body.
If you wanna stick with outlook Express..... one way would be to stick the image(s) in a folder and zip(compress) the folder. Then send the folder as an attachment and, walla! No Image in the text body.
Another way is to change the extension of the image from ,jpg (or .bmp, gif) to anything you like - such as image.abc OE will not recognise this as an image and sent it as an attachment only, but the recipient has to be aware of this and be able to change the extension back to whatever.
btw, just because the mail arrives with the image as an attachment and in the text body does not mean that the mail is nearly double in size, the image is only send once.