Did you do anything to feed power into the 770?

The USB host port on a powered hub is not supposed to actually provide power to the computer that you're plugging it into - it's supposed to _get_ power from that port. Normally, the power that goes into the hub is only used to power the gadgets you plug into the hub, not the hub itself.

If your hub provides power upstream to the 770 without something like a three headed cable - that is, if just a gender changer works - then your USB hub is totally violating the USB spec. It's convenient when they do that, since it makes it easier to use them on the 770. However, don't be surprised if most of the hubs _don't_ work.

Also, just to clarify a bit, the 770's USB chipset is designed to work as a host or a device. However, if you (where by "you" I mean an electronic engineer building a device using the chip) want it to be a host, you are supposed to do two things:
1. Include a 5v power supply in your design.
2. Use a different connector. There's a USB standard connector that works with the standard cables that the 770 uses now, _or_ a cable that connects it to other USB _devices_.

USB host mode on the 770 is there because the component that Nokia chose to use happened, conveniently, to have features that they didn't really intend to use. They were cheapskates and skipped those components.