import os
os.startfile("C:Documents and Settingsflow_modelflow.exe")
import sys, string, os, arcgisscripting
os.system("C:/Documents and Settings/flow_model/flow.exe")
##### Sol_1
import subprocess
subprocess.call(["path_to_exe.exe",'parameter_1','parameter_2'])
##### Sol_2
import os
os.startfile("path_to_exe.exe",'parameter_1','parameter_2')