No problem
Remember the correct order:
- mounting partition as /and
- removing previous /and contents
- extracting tar.gz with all files to /and
- installing the kernel (NITDroid partition must still be mounted as /and this is important, because the .deb file with NITDroid kernel installs some files to /and)
- unmounting /and
- rebooting and checking if it works

Good luck

P.S. Really, what country are you from and what's your mobile operator? Try searching and posting it in http://forum.nitdroid.com , maybe others have similar problems and found a solution