Download the files here
(I forgot to include nandpro get that here
Extract the rar, and open up the nandpro folder
install port95nt.exe (if running vista or 7 set it for compatibility mode for xp.)
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.
If during the dump it has trouble reading blocks, don't worry. You only have a problem if can't read block after block, which means something went wrong in the middle of the dump and you have to restart it again.
If you are having issues having nandpro detecting it, go over and double check all of your soldering. If you skipped out on the diode, try adding one, and just restarting your computer has fixed the issue quite a few times for me. You also want to make sure your cable is short as possible.