Classic App installation on Mac OS X

[MayheM]

Ok I work in a school and this student has been working on some T Shirt designs and was using GIMP. So I offered to give him an old version of Illustrator that the school no longer uses. The problem is he is on a Mac running Leopard and the version of the program is Illustrator 10. When I tried to install it it tells me that it needs to run as a classic app and that option is not installed. So...

How does one go about doing that? I know there are some Mac users out there...