Random Integer for Text Field

Hello, I would like to populate an empty text field with a 5 digit
random integer upon an ajax request. I am new to programming and this is
all I have so far:

rand()

It will be used for my _form.rhtml partial (a persons 5 digit ID number)
so I'm wondering if something like this would belong in a helper, model,
or view?
Thanks for any help!

helper or model depending on the day I suppose... but I'm not sure I'd do this... just because you use rand() doesn't mean that it's going to be *unique* and I'm guessing you'd like your users 5 digit ID numbers to be unique, yeah?

Just something to think about....

The ID number will mainly be used to keep track of the person's
attendance. The person will check in via USB numeric keypad and if the
5 digit numbers are too close or similiar there is more room for error
(checking in wrong person because numbers are so close). I figured if
the numbers are random they will be spread out more from each other and
hence less room for error. The number of people will most likely be
under 500.
To make each ID number unique I could use a validation for uniqueness.
If there is a better way to do all of this please let me know. Thanks!