Pass Value Between PHP & Javascript

Hi ,

i want to send the value from php to javascript function as argument , and return the result from javascript to php.. 

you can do that with ajax, I use Xajax (great library)

can you tell me link ,where i found  help about Xajax (great library) ?

???
http://www.google.com/search?hl=en&q=xajax&btnG=Google+Search