Gmail+Chrome users on XP/Vista are in for some hard times.
Google Chrome stopped supporting XP/Vista several months ago. You could continue to run an older version of Chrome even though not running a current browser would leave you at risk to its security flaws. (Note: Version 53 is the last supported version for XP/Vista. You can download it here.) In September, Firefox will follow suit.
Starting February 8, Gmail will no longer support those OSs. Gmail does have an "HTML version" that users can select and will automatically redirect users to that version in December of this year.