Another way: You may set the SUID bit to those programs, owned by the user you want them to be run as. So, if you have programe1 and programe2, and want them to be run as user1 then:
Code:
user2> ls -l programe1 programe2
-rwsr-xr-x 1 user1 user1 0 Jan 17 11:26 programe1
-rwsr-xr-x 1 user1 user1 0 Jan 17 11:26 programe2
user2> ./programe1