If you go to school, you can do CPT.. CPT can be done for as long as you are in school. One of my friends has been working for a company for three straight semesters (part time).. she will graduate this semester and will start her OPT.
I mean, it depends on the school, but most schools let you do an internship for multiple semesters as long as you fulfil the 12 credit requirement if you are a udergrad and 9 credits if you are a grad student.

Hope that helps.