A new version of Nand Pro has been released a few days ago. It's a PC tool that allows you to read and write on the Xbox 360 NAND via USB or LPT with some simple wiring (for LPT at least).
From the readme/nfo:
This release fixes a bug when a sector fails to write, ie it will retry the block now.
Before it could corrupt the rest of the write. Reading was unaffected.
Also new feature, allows a "virtual nand device": Which is a RAW file, that nandpro pretends is a nand
It can then extract/inject individual blocks from a image, instead of a nand (ie no hardware)
For example you could inject a small xell into a large image with the following:
nandpro completerawimage.bin: -w16 xell.ecc