I have a Deluo GPS receiver that I'd would like to use with an N770 to access either MS Streets & Trips lite or Google maps. The GPS requires a USB port. Is there a stepdown device that would reduce the male USB plug to fit the tablet's female port? ... and if so, would this be likely to work. Would the alternative be to purchase a bluetooth GPS receiver?

Finding an adaptor is not your problem. I have a N800 with the proper adaptor but cannot use my USB GPS because you need to find and then install a special device driver. It is much easier to just buy a Holux M1000 or similar bluetooth GPS. One other thing, my USB GPS would also drain my battery.

I don't think drivers are an issue. Most (all?) USB GPSes are USB-serial internally, and there are drivers available for several usb-serial chipsets. Some Deluo models, at least, use a Prolific 2303 chipset, and I know the pl2303 driver works fine with my USB-RS232 dongle, so I'd try that one. Battery life on whatever's powering the USB will suffer, but several people are using USB GPSes, and I'd bet yours would work too.

To answer your question directly: Yes, but... it's complicated. On the N8x0, the USB port can provide power out, but for the 770, you actually need your adapter to supply power up to the 770 as well as downstream. So some sort of power injector is needed. This also moves the battery drain from the N800 to your power injector, so if that's big enough, your tablet battery life should be relatively unchanged.

As to the actual construction of a 770 power injector, there's info all over the net, but as a non-770-owner, I'm fairly ignorant of the variations, and will leave that to you and Google. AFAIK, you will have to build it yourself or get someone to custom build it. For the N800, there's an adapter available pre-built from electronicproductonline.com, which is a standalone solution for the N800 and might be useful as a component in a 770 solution.