The simplest way of handling the issue is upgrading win2k pro. Win2k pro specifically deals with this issue.
If you are set on Win98 do the following carefully:
To add additional IP addresses, use Registry Editor to edit the registry. Go to the following registry section:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\NetTrans\
There should be multiple subkeys with the value 0000, 0001, and so on. If the computer has only one network adapter, click the 0000 entry. You should then see a value named IPAddress and a value named IPMask.
For each additional IP address, add to the two values.
The IPAddress value should contain the current IP addresses. This value is a string of IP addresses separated by commas with no embedded spaces. The IPMask value should be a list of comma-separated subnet masks with no embedded spaces. You must add a mask value for each IPAddress. When you are done, quit Registry Editor and then restart the computer.
I would advise having computer support at your work (if available) help with this process.
Good luck!