Is it possible to run several different versions of Oracle on the same server machine?

The Oracle (tm) Users' Co-Operative FAQ

Is it possible to run several different versions of Oracle on the same machine

Yes! We can run different versions of Oracle on the same machine provided that Oracle_base_directory is same for both the versions. 

Oracle_base_directory is the directory where oracle is installed like C:\oracle or D:\orant
Under the Base directory Oracle home directories are differentiated like
C:\oracle\oracle8
C:\oracle\oracle9
In short you can have different versions installed on the same machine if they are installed in the same directory.

Further reading:  N/A