PKTKKG, do it thusly:
When you've clicked reply/new post, you'll see the smileys, buttons and whatnot. One of the items is the IMG button to post images. It places (IMG) ...(/IMG) either side of the text pointing to an image. What goes in between the tags, is a web address pointing to a graphic.
So, the graphic needs to be up on the web. Most free hosts like geocities won't let you link to pictures on there from external sites like GreekChat so you'd either have to point to a picture on a paid host (like a commercial/national site) OR if you just have some pics on your hard drive and no website then use a site which
does let you upload pics and then link to them. www.photobucket.com is a decent one for you to try, pretty easy to use.
If you see a pic you like on a webpage out there (non-geocities etc sites) then right click on it and select properties. You'll see the web address of the actual pic, starting with http://. Highlight it with the mouse and copy it all (ctrl-c, or copy via menu). Then come to your post and that's the text you'll be putting inside the (IMG) tag.
Example: {IMG}http://www.website.com/rush/pic101.jpg{/IMG}. So then click submit reply after adding any caption or text and people will see the pic in all it's glory.
Summary: If pictures not already on a website then use something like photobucket.com. Then get the webpage address of the specific pic and then post a message on here with the entire webaddress (called a URL) in between those IMG tags. Oh and make sure it doesn't have {IMG}{URL} ...., i.e. both tags - you just need IMG tags either side.
Square brackets [] not 'curly' () ones are used when you press the IMG button in a real attempt of course.
edited to add: After posting I found this useful page which describes how to do it in quick simple terms. The above post contains some useful pointers on getting images so you can put the code in though, so I'll leave it up.