Hi
Sounds like your network configuration needs tweaking, or your network card/driver needs checking.
Open the network applet in Control Panel, select the TCP/IP entries then click properties. Make sure that TCP/IP configuration matches that of the other computers. If you have assigned a static IP address, make sure the address is correct. Check any other settings such as DNS if relevant. Make sure the name of the computer is unique as well (on the Identification tab).
If this is OK, then I would open Device Manager (Right-click My Computer, select Properties, then click the DM tab), and check to see if the network card is working properly. You can attempt to reinstall the drivers, though in my experience this often does not work.
Uninstall the drivers for the network card, remove the card from Device Manager, switch off your computer, remove the network card, then reboot. After it has rebooted, switch it off, and reinsert the card, making sure that it is firmly seated in its slot. Reboot, then when (or if) Win98 detects it make sure you insert the disk with the drivers on it, and install the drivers from the disk (ask windows to display a list of drivers, then click Have Disk). If Windows does not detect your card, use Add new hardware wizard in Control Panel.
Use the ping command from a DOS prompt to ping the IP address of another computer (Ping 192.168.0.10 for example). If this fails then you may need to replace your card.
Good luck