Restore a ROM Back-up
It's really that simple. :)  

And you wouldn't even have to do step 4 (because your NANDROID backup is like taking an image of your phone, that includes all installed apps and data too).

If you wanted to do a quick test, you could try installing one app, then restoring to your NANDROID backup.  When it's done, it should no longer have that one app  you installed.  And it'll also show that your backup is good.