Infrastructure Software

Hello: I would like to know what is the best way to execute a script owner by a different unix user?
Right now, we run one process using one user; and then do a su manually and run the second process using a different user account ....I would like to automate the process......
I can make the second script executable to all user.... but then I will have to change the code to handle the shell variable etc... su is good, but I have to manually type in the password, and run the script....
Is rsh a good candidate, even though the 2 accounts are on the same box?

Thanks