Logon Script Not Working

Ok here is the setup. NT4 Domain and NT4 workstations on dhcp with 3c905b or c network cards, HP PIII all MHz 128mb memory min 256mb max approx 411 PC?s. 1 PDC and 2 off site BDC?s.
Ok here is the problem. On certain computers when anyone logs in for the first time since a reboot 3 of the 4 drive mappings don?t work. If they log off and back on it maps all the drives correctly. This happens in different places on the network. It does not follow the computer if you move it to a different place.If you replace the computer it does not happen. New network drivers have been installed. TCP/IP removed and reinstalled. Well that is all the detail I can think of so what does everyone think?