Loading a webpage at a paticular part rather than at the top

Hi

Ive noticed on many webpages, that on occasion you can click a link however rather than loading the webpage with the scroll bar at the top (ie you start of at the top of the webpage) you can start on a specific part of the webpage, for example half way through?

I am using PHP, HTTP and mysql, and require that certain webpages load up more than once (for example on a form where someone is signing up but enters an invalid password) and rather than the page starting at the top, I wanted it to start at the beginning of the form?

Is this possible, or do i require some sort of plugin or extensions?

Thanks