If you create a gmail account, you will have a google account with two email addresses attached to it, your usual one and the gmail account. In order to preserve your groups and your identity, you must delete your usual email id from the account and create a new google account under that email id. Oddly your groups will still be waiting for you under your usual email. Gmail is pushy. It takes over from your regular email client, whether you want it to or not. The only way I can think of to keep gmail properly secondary is never to set up a gmail account in the first place.