Option 1: The best way to include pictures in messages is to upload them to a Web-based photo sharing site. I recommend a free site called http://photobucket.com
but there are plenty of other choices.
A nice feature about PhotoBucket is they provide the "Img" BBCode text for each picture, which you can simply insert into your message. It's as simple as copy and paste.
Option 2: For smaller images, you can attach up to 3 to the message under the "Upload Attachment" section. While composing the post, you'll have an option to display uploaded images "inline," though there are file size and resolution restrictions not present with Option 1.
The forums support file attachments for common extensions such as audio clips, video clips, .pdf, .doc, .xls, and .ppt for sizes up to 1 meg per message. If that doesn't get the job done then you can always post an FTP link instead.
Moderators check the attachments for content and ban users who upload malicious files. Please be advised that when you download a file it's at your own risk. Be smart and always make sure to use virus protection software.