Hi
I would expect for example
"C:\Program Files\PSPP\PSPP.exe" %mysppsjob%
to do the job. You will need another tool to change "@datafile" to "%DATA"%". At least I am not aware PSPP supports "-symbol @datafile %DATA%".
However the environment variable %TEMP% has a special meaning. (Usually it is equal to %TMP% on MSWindows) I don't know what happens if %TEMP% points to a file instead of a directory nut wouldn't do that. I am more surpressed that your PC doesn't crash as that this doesn't work correct.
Have fun