Googlemail changing to Gmail issue, help please ?

I'm trying to help my friend's mum with her Googlemail account, I've only ever used Y! so am not too sure about stuff.

She can't login to her old Googlemail on the new Gmail page, she said she'd been getting messages that it was changing to Gmail but she wasn't sure what to do.

Should the old Google email address still work ok ?

When you log in can you just enter the username like with Y! or do you need to enter the full email address ?

Is it now @Gmail.com ? (or co.uk )

Could she have somehow opted out of the changeover ?!

Any ideas please ?

Thanks.