File access slow on windows XP, STATUS_OBJECT_NAME_NOT_FOUND

on those clients, try moving the Microsoft Windows Network to the top of the list in the network provider binding order

How to change the Provider Order

1. Click Start, click Run, type ncpa.cpl , and then click OK.
You can see the available connections in the LAN and High-Speed Internet section of the Network Connections window.
2. On the Advanced menu, click Advanced Settings, and then click the Provider Order tab.
3. Use the arrow keys to move the Microsoft Windows Network provider to the top of the list and select OK

I have seen issues where mixed Netware/Novell environments tend to fight each other a bit, the battleground is the Provider Order tab.