This is a little tricky, but seems to work for most of users.
You must run a classic environment in the same partition of your current copy of OS X and use a code similar to this:
tell application "Classic Application"
using terms from application "HD:System Folder:Scripting Additions:related osax"
-- use here osaxen commands
end using terms from
end tell
Where “Classic Application” is a classic application (eg, a stay-open applet) and “using terms from” targets the osax you wanna use (located in the regular OS 9 scripting additions folder).