how can replace some of words when I added post from ..

hi ,
my friends ..

I want to design a small plugin ..

it is work is: when the user write a post for example :

<<WordPress>> widgets are the dynamic objects which eases the customization of the content on <<sidebars>> and widgetized <<footers>>. <<Widgets>> allows drag-n-drop interface in the Dashboard <<admin panel>>, for easy <<management>>.

directly the plugins search about the words which between <<..>> then search in the db_wp if there a title like this word.
if it exist replace it by the url of page ..
if it not exist create a new page with some ‘text .. ect’ then replace the word by the url of page.

for example : when I wrote these: <<wordpress>> widgets are the dynamic <<objects>> .
the plugins search about ‘wordpress’ in the title pages if it existe set the url: wordpress. then the plugins search about ‘ objects’ in the title pages if it not exist the first step: create a page: object then fill it some text the final step . replace the word <<objects>> , objects ,

I want to know how to do it.
Give me example I will try to develompe it .

Thank you very much ..