Basic Script, I added one for Bye as well. Enjoy :)
on :text:Hello:#: {
set %reply $rand(1,5)
if (%reply == 1) { msg $chan Hey there }
elseif (%reply == 2) { msg $chan Hey }
elseif (%reply == 3) { msg $chan Hi! }
elseif (%reply == 4) { msg $chan Hello }
elseif (%reply == 5) { msg $chan Hey there, $nick }
}
on :text:Bye:#: {
set %reply2 $rand(1,5)
if (%reply2 == 1) { msg $chan Good bye }
elseif (%reply2 == 2) { msg $chan Cya }
elseif (%reply2 == 3) { msg $chan Take Care! }
elseif (%reply2 == 4) { msg $chan Bye }
elseif (%reply2 == 5) { msg $chan Peace out, $nick }