Or a link to the Nokia RX-51/N900 Service Manuals for detailed information on disassembly; combine that with whichever approach to the USB port fix takes your fancy. I'm about to do this on one, maybe two N900s, and think I favour using a thin "worm" of epoxy putty around the sides and the back of the port, reinforcing the pads and at the same time filling in the space under each side of the USB port. In theory (I haven't done it yet), this should adhere to more surface area than solder and will physically fill up the "triangular prism" spaces under each side of the USB port to provide a mechanical buttress against movement. We shall see...