champ is right. let me make it more clear, you need visa just to enter the States. as long as your visa isn't expired, you won't be stopped anywhere. after you enter, your I-20 is the key, i.e. as long you have a valid I-20 and you are maintaining your status, you can live tenson-free. but be prepared to apply for a new visa next time you go home (anytime after Feb 2012) because you'll need one to enter back.