Dear Friends, I need a Help. how can i create a new user in linux from a already exist user account ( not ROOT user ). ie. using setuid() function i have to activate the user as root user tempararyly and create one user. and also change the file permission ( to write ) which is also created by root user.

Foggy question, IMHO. And -as stated- deserving an answer along the lines of "you can't". Also, still IMHO, if you have to ask you don't want to mess w/ this kinda stuff, believe me.

its urgent please help me.

Generally this doesn't buy you anything. Good of you not to have put that into the Subject.