I dunno if this has been addressed or not....

Newer Macs have the ability to run OS Classic as a session within OSX. This would still allow you to access the original documents within the older Mac OS (I'm assuming you're talking OS 7, 8, or 9 here).

Another option might be an external drive enclosure, wherein the hard drive is actually taken out of the old Mac, and dropped into an external enclosure which can be then connected to any Mac or PC via USB (or Firewire if the new computer has it)-I'd recommend checking with any local Apple stores' genius bar or service centers which should have similar personnel.