If the picture is saved onto your harddrive, use the browse option below the text box in the "reply" screen.
If it is not, get the address to the picture (right click, properties, copy adress), and you may insert it into a post with the tags [img] [/img]
For example, I will use Abe's Son's sig:
Address:
http://img91.exs.cx/img91/2678/abess...ignatur6vg.gif
when combined with the image tags: [img]*http://img91.exs.cx/img91/2678/abessonstarcraftsignatur6vg.gif[/img] (remove *)
final product:
If the picture is a screenshot or a picture you made in a program such as MS Paint, you will first need to host the picture from a website, and then repeat the steps mentioned above. To host a picture, use either
www.photobucket.com
or
www.imageshack.us (my personal favorite)
NOTE: if you use the attachments option, the picture will be posted at the end of your post, but if you use the Copy + Paste address method, you can put the picture wherever you want in the post (like above)