No, using su, it would be su -c "/sbin/shutdown -h now"
But you can just press CTRL+ALT+DEL to reboot
And sudo is not su. with sudo you can specify a user and a given program that the user can run as root wiithout entering a password..
f.e. as root
then find the line where is:
# User privilege specification
root ALL=(ALL) ALL
And below that you can add your entry... f.e. allowing user foobar to execute shutdown without passwd:
now foobar can just enter "sudo /sbin/shutdown -h now" and he must not enter a passwd..
for lazyness, you could add an alias to your .bashrc or .bash_login, say
alias shutdown='sudo /sbin/shutdown -h now'
re-login and 'shutdown'