How to - Fill a field on a CDO with a unique, random code?

Hi,

We would like to fill a field on a custom object with a unique code - This can be a copy of the CDO ID, but we need this to be on a field so that it can be field merged.

This custom object is being created by a form, we have considered adding some Javascript to the form to fill in a hidden field on form submission that can then be added to the custom object. If anyone has experience with this, some examples or explainations of the process involved would be appreciated.

Requirements:

• Data needs to be unique (Cannot use raw customer provided data)