You are not telling us what the problem is or what sort of error
messages you are getting so it's hard for us to give you focused
information.  A few things that you should keep in mind and adhere to:

1-  Completely turn off all firewalls while you attempt to setup the
network.

2-  Use a common protocol and use the fewest protocols possible.  You
should be able to use TCP/IP only, NetBEUI is seldom required.

3-  *Use* *authenticated* *logons* on the Windows 98 box!  Assign
usernames and *passwords*!  Use logons on the Windows 98 box!  Windows
2000 is a secure operating system that requires proper credentials and
authentication in order to access it's resources.  Don't try to bypass
this on the Windows 98 computer.

4-  Create user accounts with identical usernames and passwords on the
Windows 2000 computer.

Try these for more help and information:

http://www.windowsnetworking.com/articles_tutorials/w2kwin9x.html
http://chicagotech.net/

John

Two questions come to mind.

"Did have it working" - what changed?

How are IP addresses assigned?

Here's a basic reference page with some hints:

http://peoplescounsel.orgfree.com/ref/gen/security/NETWORKING.htm

Right click My Network Places on the Desktop.
Click Properties.
Right click Local Area Connection.
Click Properties.

Under "This connection uses....."
Click "Client for MS Networks".
Click Properties.
Select "Windows Locator" from the dropdown box.
Click Ok.

Scroll to and select Internet Protocol (TCP/IP).
Click Properties.

Under the General tab make sure "Obtain an IP address automatically" is selected.
Click the Advanced button.

Under the DNS tab:
Selected "Append Primary and Parent  DNS suffixes.
Register this connections address in DNS"

Under the WINS tab > NetBIOS:
Selected Default.
Ok out of MNP.

Reboot if required.
Open a command prompt, click Start > Run, type in:  cmd  and press Enter.
At the prompt type each command below and press Enter after each.
**Note:  Command noted by =,  Space noted by ^.  Do not type the = or ^.

=ping ^ 192.168.1.1      *Routers IP, change as necessary.
If it times out then there is no communication between the router and machine.
If not then the machine communicates with the router.

=ping ^ google.com
If it times out then there is no connection to the net.
If not then net connection is established and all is well.

ping 127.0.0.1
If it fails it may be a TCP/IP stack problem.

Ping each computer from the other using the UNC:
=ping ^ computername
If it fails either way there's an IP or Name resolution problem.

If pinging times out on any address, to see if the  machines IP is correct along with
other settings.
= ipconfig ^ /all
If anything isn't correct, at the prompt type and press Enter after each command (98
may be different):

=ipconfig ^ /release
=ipconfig ^ /flushdns
=ipconfig ^ /renew
=ipconfig ^ /registerdns
=exit
If that fails reopen the command prompt, run release and flushdns only and exit.

Shut down the machine.
Pull the power from the router.
Pull the power from the modem.
Wait approx 30 secs.
Apply power to the modem and wait for it to finish synchronizing with the cable.
Apply power to the router and wait for it to finish synchronizing with the modem.
Power up the machine.
The machine should now be assigned a new IP from the router.
Run ipconfig or attempt net connection to test.