Here are some places where you can look for information about NIfTI:

Homepage
NIfTI has a homepage that can be found at http://nifti.nimh.nih.gov
Forums
  1. nifti2_data_format: A 64-bit update to the NIfTI format
  2. extending_nifti: Extending the NIfTI format
  3. nifti-open: Nifti Open Discussion
Wiki
NIfTI has a wiki that can be found here.