The syntax could be
Host('ifrun60 custform.fmx scott/tiger statistics=yes paramters');

Say this form has a parameter "DNO" thru which it displays the form. So in the calling form using host command u'll write:
host('d:\orant\bin\ifrun60 empdetails.fmx dno='||:deptno);

similarly u can try for passing parameters to other executables.