A couple of options.
Get somewhere to host the pictures, such as imageshack or photobucket, upload them then post them on the board like this:
http://www.the_image_url/image1.jpg[/ímg]
[img]http://www.the_image_url/image2.jpg[/ímg]
[img]http://www.the_image_url/image3.jpg[/ímg]
Or use the the 'File Attachments' fuction and the bottom of the page, then submit the post, then edit it and attach another image, then submit the post, then edit it and attach another image, then submit the post, then edit it and attach another image, then submit the post, then edit it and attach another image, then submit the post, then edit it and attach another image....