message board multiple posts

I have written a simple message board using php/mysql. The form to enter a new post is in the same file as the code to display the forum, so that when you submit a new post, it goes back to the same page and displays the new post.
After posting a message, hitting reload in the brower reposts the same message again, since the broswer has cached the form's contents. How can I prevent messages from posting again if the user reloads the page?

i am a new user to this site ...i don't know hot to post the message that is why ia m replying to this and asking aquestion..

how does one transfer data from one mysql databse to the other mysql database using php on the same machine..if any one can give me the code i will be grateful

thanks
ravi