Upload your images to a web-accessible address. Many ISPs allocate customers some storage space for web pages, images, files, etc. Use an FTP program or whatever means your ISP suggests for the process. If you don't have web space, you can upload your images to any of a number of free hosting services, like PhotoBucket.com
Once the images are uploaded, link them into your posts with the following format:
If that seems like a lot of effort, just click on the little "Insert Image" icon in the posting tools window.