Make sure that your Win98 machine is set up to use the Windows Network Client logon and not just the windows logon. Then create a logon name (use a blank password and it won't ask you each time you reboot).
On your Win2K machine, go into the control panel and then click on the "Users and Passwords" applet. Create a user account with whatever priviledges you want them to have, using the exact same username and password you set up on your Win98 machine.
After you've restarted both machines (not actually necessary, but not a bad practice) you should be able to attatch to shared resources from your Win98 machine. The problem was that your Win2K machine has no idea WHO your Win98 machine is. If you were in an environment where both were clients on a network with an authentication server, then they would already "know" each other... but since you don't have that environment, your Win2K Pro machine will only allow people with accounts to attatch to shared items.
Joe