LAST EDITED ON 04-15-02 AT 03:07 PM (EST)EDITED because I didn't actually answer the questions before hitting enter...
First of all.. to post a picture, after hitting reply, you'll see a link with "Click here to upload your file"... this link will appear above the field in which you type in yoru message. Click on that link, and fill in the appropriate information, then click "Upload file!"
When you're done, you'll see a URL displayed in that window (something like http://community.realitytvworld.com/boards/User_files/3c58918d470e4783.gif)
Simply copy and paste this link into your message, and the forum software will automatically display the picture in the window.
As for size, it depends on what you're posting. There is a maximum FILE size of 80kb, so you shouldn't post anything larger than that... if what you're posting is a sig, it should be considerably smaller, obviously. If it's a vidcap, a typical size is 320 x 240 pixels. For other spoiler-related things, use your judgement.
You never know what might be up my sleeeve...