Before installing WSPM, check that

• Matlab is correctly installed
• SPM is correctly installed
  At the Matlab prompt, type:
  >> which spm
  If the filename spm.m is returned, SPM has been correctly installed

The installation of WSPM is very similar to most other SPM toolboxes:

• Download the tarred gzip.
• Extract the archive in your SPM/toolbox directory: tar zxvf WSPM.tar.gz
• Start SPM; it should recognize automatically that a new toolbox has been installed and add it to the 'Toolboxes' drop-down menu