OS 9 / OS X.2 File Sharing
This is a quick, terse walkthrough of screenshots taken
under OS X 10.2.8 and OS 9.2.2 to set them up for mutual file sharing using a crossover cable.
(This procedure appears almost exactly the same for OS 8.5 and OS 8.6 systems.
The control panels used are almost identical, and differences seem cosmetic.)
If you already have successfully set up a home network with a router or hub,
you can use these instructions for an existing network instead.
If you prefer to see the screenshots for OS X 10.3 Panther instead, see my OS X 10.3 walkthru here.
Another excellent resource is to simply type "file sharing" into OS X's Mac help (Finder's Help menu.)
Pertinent AppleCare KnowledgeBase articles
OS 9 / OS X File Sharing
You will need to connect the two Macs together in a network.
A direct Mac-to-Mac ethernet cable, a hub, switch, or router can be used,
though this page does not assume a router or concurrent Internet connection.
Here's an Apple KBase article that covers tha basics and has links to both OS X and OS 9 info.
(If you are running a cable directly between two Macs, see this article to see if a cross-over cable is necessary for your Mac model.
New Macs with 100BaseT ethernet have autosense that can work with either a straight-through or a cross-over cable.
Older 10baseT Ethernet Macs will need a crossover cable.)
If this is a temporary set-up and you change your existing network settings, remember to make a note of what the old settings were so you can restore them when you are done.
With OS X you may wan to make a new Network Location for these temporary settings to it's easy to go back to the current settings.
Try this process on the OSX system:
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In System Preferences' Network pane:
Select System Preferences / Network pane.
Set the "Show" pull-down to "Network Port Configurations"
Uncheck Irda is it's present.
Select Built-in Ethernet and click and drag it up to the top of the list (the order determines which port gets preference.) It should be checked.

.
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Set the Show pull-down to "Built-in Ethernet"
Click the TCP/IP tab.
Set the "Configure:" pull-down to "Manually".
(If "manually isn't an option, go to the PPPoE tab and Uncheck the "Connect using PPPoE box.")
Enter an IP address. This should match the OS 9 system's subnet or your Router's subnet, if either of those are assigned.
It also must be different from the IP Address you have/will assign to all other computers you are connecting to your home network.
If you've never picked one and aren't going to use this for an ethernet connection, borrow mine: 192.168.1.20 .
(If you have more than one system, use other addresses with the same first 3 numbers, e.g. 192.168.1.21, 192.1168.1.22...)
Set Subnet Mask to 255.255.255.0.
(Leave Router and DNS info blank if you don't have an internet connection.)

(your Location will probably be "Automatic".)
Click Apply.
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Click to the Appletalk tab. Check "Make Appletalk Active".
(This enables file-sharing with older Mac OS 8-based system;
you don't need to do this if all your systems are OS X.)

Click Apply.
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"Show all" System Preferences and pick the Sharing pane.
Click on "Personal file sharing." Click Start.

Your computer's name will be displayed instead of mine.
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(This step is only necessesary in OS X 10.3 Panther if you are going to use it with a OS 8.6 or previous version of MacOS)
Launch Directory Access application from the Utilities folder.
Go to the Services tab.
If the padlock icon at the bottom of the screen is locked, unlock it and provide your administrator password.
Then check the Appletalk box to make it active.
(This enables file-sharing with older Mac OS 8-based system;
you don't need to do this if all your systems are OS X OS 9.)

Click Apply.
On the OS 9 system:
(This procedure appears almost exactly the same for OS 8.5 and OS 8.6 systems.)
-
Use the TCP/IP Control Panel. Set user Mode to Administrative if not already unlocked.
On Connect via: pull-down select "Built-Ethernet".
On Configure: pull-down select "Manually"
For IP Address, enter what you use. If you haven't picked one previously, borrow mine: 192.168.1.22.
Set Subnet mask to 255.255.255.0. Router and name server can stay blank.

, but with DNS info blank.
Close and click Save.
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Open Appletalk control panel.
On Connect-via pull-down choose Ethernet built-in.

Close and save.
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Open FileSharing control panel.
If you don't have a name, password, or computer name, make some up.

Click "Start".
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In Finder, select your disk drive icon, then "Get Info..." from the File menu.
Set the Show: pull-down to Sharing.
Check the "Share this item and its contents" box.

Your Hard disk name will show inseat of my default "Macintosh HD"
Close
On the OS 9 system:
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Select Chooser, click AppleShare, wait a few seconds.

(Your OS X system name will appear instead of mine.)
The name of your OS X system should appear. Double-click it.
Use your OS X short user name and password, as registered on the OS X system, to log in.
The shared OS X disks/folders should display. Click to mount.
On the OS X system:
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In Finder select "Connect to Server..." from the Go menu
(or Open a Finder window to the Network icon.)
-
A list of systems on your local network should appear.
Pick the OS 9 system. Use the Name and Password you set on the OS 9 system
(in its FileSharing control panel) to log in.
A list of the mountable disks should appear. Pick the one you want and click OK.
Your OS 9 system's disk should mount on the Finder desktop.
Good Luck!
You can check the rest of my home network config info here.
If something above seems missing, confusing or down-right wrong, you can eMail me as car1son at my .Mac account.
(Please be specific at what point things went wrong and how they went wrong.)
Good luck!