hey bro you are going to love it, it should not be very difficult if you are already in the US , but if you have somebody in europe ask him to send an invitation ( sort of) in letter, saying that you could stay wiih them, or else you have to show hotel reservations , also you have to book ( not purchase) a return ticket .it should not be that expensive , if you stay in like youth hostels ( e.g:YMCA),lot sof young guys/girls specially students they there,they are thre is most of the cities , cheap and nice good way to meet lot of girls too, you'll have a blast.