PLEASE check out AMSTAT NEWS, January 1999 Issue. There are many
internship opportunities listed there, some for summer, some at other
times of the year. 

In fact, AMSTAT ALWAYS devotes a few pages of  its January issue 
to that years' internship opportunities.

BTW, although most are for graduate students, some will take
undergraduate students who are exceptional (regardless of the
undergraduate background). So if you think you are in this category,
contact the internship administrator and survey your chances.