Everything you ever wanted to know about using Classic in Tiger here:
http://www.apple.com/support/tiger/classic/
OS 9 Support Page:
http://www.info.apple.com/usen/macos9/
I believe Classic support is now discontinued:
http://en.wikipedia.org/wiki/Mac_OS_9
"Retail copies of Mac OS 9 are still available from several Internet businesses at varying prices. Mac OS 9 is no longer available from Apple. Mac OS 9 is not yet classified as abandonware, as it is still in wide use by those who cannot upgrade to Mac OS X due to hardware limitations, or prefer it to Mac OS X."