It's very simple to read your nand. Just make sure you install the port95nt.exe (if running vista or 7 set it for compatibility mode for xp.) otherwise you won't be able to access your xbox via printer connection.
Plug your Xbox 360 in, but don't power it on.
Plug the lpt cable in
Pop open cmd and change directories to your nandpro folder
type nandpro lpt: -r16 nand.bin
It will start to dump, this will take 35 minutes
Type nandpro lpt: -r16 nand2.bin and dump it a second time.
Here is a great tutorial that I used when I first learned how to jtag.http://www.instructables.com/id/How-to-JTAG-your-Xbox-360-and-run-homebrew/step4/Dumping-the-nand/