First off, you must decide whether you need a USB host device or just slave/client - is your device meant to be connected to a computer or will it drive other USB devices like a flash drive or a printer. In first case, as Ashish says, there are '52s with USB client built in. In the other case, you won't get anywhere without the separate chip Michael mentions, unless you're up to some very hard work including some wave effects, very strict timings and such.