Try using this:
http://tinypic.com/
Click on the browse link for "File" & browse to the file you want to upload
Click on the green box: Upload Now
Copy the info in the box from the "Img code for Forums & Message boards"
See example below, It will look like the example with the exception that the beginning & ending will be like this [img]xxxxxxxxxxx[/img] I had to modify the example brackets or it wouldn't show correct in this post
(IMG)http://i47.tinypic.com/example.jpg(/IMG)
Paste the Image link into the body of your post & you just posted your picture.
You may want to save a text doccument of the image code so in the future you can post the same picture without having to upload it again!
Hope this helps,
Paul