Network Printer Not Showing in Directory

We are running XP Pro on a Win2K network. Any printers that are directly connected to the network are not being displayed in the printer directory even though the box to do so is check. Does anyone know how to resolve this? We are having problems "losing" these printers on the XP machines and they aren't always showing up on the server even though they are turned on. Sometimes it takes several refreshes on the server to get these printers to "reappear." Thanks for your help.