jQuery with PHP

[eluser]RedIgniter[/eluser]
Hello everyone,

I am trying to create a registration form like facebook has, where the user sees only one error field on the bottom, (for which I guess PHP if statements are nested and are checking for inputs 1 by 1). Anyways, how would I come across this, using jquery and PHP, where the page doesn't reload. I really need help with this, and don't got no idea where to start from. I was struggling on finding such scripts online last couple of days but didn't find anything useful, or anything that could have done implemented with CodeIgniter.

Thanks in advance, any help is appreciated.