How to generate a serial of random numbers

Hi all,

I want to generate a serial of 5 random numbers based on the size of an
array(let say the size of array is 100).
Here are the rules:1) 5 random numbers are different 2) Once they are
generated they can't appear in the next round of random numbers. What is
the better way to do this? Now what I think of is to remove the items
corresponding to the random number from the previouse array and
eventually my array is smaller and smaller. Any other idea?