Win98 networking with Win2000 server.

I have a network comprising some Win98 and WinXP pro
clients and a Win 2000 server with active directory.

All were working fine for some time but recently I have
had 2 Win98 machines unable to log in.

The NICs will all ping eachother and the shared drives
can all be seen from other machines in NW Neighbourhood.
But still users are unable to log in on these machines.

The users can log in from other machines but not from
these 2 so the server appears to authenticate the users
but not these two particular computers.

All are DHCP clients, all can access the internet via a
DSL router.

The 2 offending machines can be browsed to from other
machines on the network and files can be dragged and
dropped to and from them.

I have tried remaking thy computer accounts and deleting
thy existing ones. I have tried making new computer
accounts and renaming the clients to suit.

Any ideas please.

Simon