get logged in users ids (URGENT)

Hi,

I need to get the current logged in users ids and i really don't know how to use ws in moodle (i'm not good at ws in general). i tried some code i found on the internet, but it just doesn't seem to work each time i try to sent $USER->id and i don't know why!! i can read the variable but i can't send it to the client (i user nusoap)!!

is there some kind of restrectrion concerning the sending of user ids? should i only use the functions defined in moodle?

i would be very grateful to whoever provides me with a detailed answer on how to do it. 

Thanks a lot.