Is there a way to set a cookie to a users machine that will remember his login information as well as his preferences for which ever theme he likes to view the site with?

I have over 1100 registered users at vmoa.net many of them find it a hassle to have to always type in their passwords and then switch to a different theme.... The default theme was choosen by the president of the organization... I am adding alternate themes as they are suggested... I am only the webmaster... and can only implement technical changes not content...

Later/wetsteve