You can re-size it and then try to post it.
I have been using
www.moviephotoforums.com to host my photos. You can upload HUGE files and it will automatically give you a scaled down version you can post on forums when you view the photos in your "albums." The photo below is some 7.2 mega pixels. The forum provides code so you just cut and paste it into your thread. Works great with vBulliten Forums.
Give it a try.