refresh forms textfields with whats in mysql

I am creating a chat script.

I wish to have the textfield in a form updated to show the contents of that in a mysql database.

at present i am using the meta-refresh which is not working as this causes problems with new entries being added.

how best should i do this?

Ajax technology is probably the best way.

i have been looking all over where ever i can to find out how i do this.

i have only found one thing that works but is not what i was thinking it was.

a sort of check username exists script when you start to type in text in a field it would show a message that the username exisits
when the 'keys are up' no typing it does a single check for this name in a database using another php file.

but this is not what i was after,

i have been told in other forums that i should be looking at ajax but have no idea where to look or where to start to get anything working.

i have even put a post in a 'hire a programmer' but no takers as yet!

do you have any knowledge of ajax ?