With ref to adding custom fields to WP admins/users

Hi

I am converting a standalone PHP script to a wordpress plugin.

Now this script has one table for ‘users’ and one table called groups which basically defines if a user is a user, admin or a guest.

There are some fields in the users table which are not there in the default WP users table.

What I want to know is, what is recommended in general for user table in WordPress plugins–> should I modify the WP users table and add my fields to it? Or should I create a separate table containing the extra fields and link this table to the WP users table correctly? Which approach do you recommend out of the above (or some other approach if I have not thought of that) and why do you recommend it?

Thanks,

Arvind.