Mike, this device will work exactly the same way for the Nokia 770 as for the Sony PSP - it's a self powered hard drive enclosure with USB host capabilty... Here's another:
http://macally.com/spec/usb/storage_...hr_250otg.html

Also keep in mind that the 770 can be set to be USB host but the PSP can't - I also have a PSP so I've tried hacking it too