[wp-hackers] Accessing jQuery in Core for a plugin

[ade]

Hi all,
 
I'm writing a plugin around a jQuery script and I'm trying to understand how best to access jQuery which, if I understand correctly, is included in the Wordpress core files.
 
My question is this: in my plugin, how do I register my js script to use the core jQuery? Am I right in thinking I use wp_register_script within an init function? Or do I use wp_enqueue_script? And if I use the latter, will this prevent jQuery being loaded twice if it is already called by another installed plugin? Yes, I'm confused. :-)
 
If there isn't a quick and easy answer, a link to any articles out there would be much appreciated. 
 
Thanks!
 
Ade.