I changed the value to 600, will be changing to 800 today when I check the code again. I think I'll have a friend look as well to see if I'm missing anything obvious. Images are inserted via the [ img] [ /img] tags.
In case it helps this:
http://shoandgo.com/gallery/albums/album23/100_0491.jpg is one of the test images th at I used. (Warning: Quite large)
I've only tried with vb tags, should I try HTML as another test?