ATT interent(DSL), and their modem?

so i was trying to order the Xtreme dsl and when i got to the modem part i was confused. There is no way i intend to pay $75 for a modem. and the littel chat lady made it seem like i was going to just be ruined if i wanted to try to find something cheaper..I also have vista and I heard that some other modems wouldnt work with it.. Does ATT rent modems? and will watching movies online exceed my bandwith? and another thing i dont plan to be at home very long (like 3 months at the least) so is there some month by month system offered by ANY internet companies??
***serious answers only please.****

cable tv | dsl internet | phone customer