network – W98 sees XP but not vice versa

Twice, I’ve encountered this situation.
An XP machine and a W98 machine networked together in the same workgroup. The W98 machine can see the XP machine, but not vice versa.

IP addresses are unique, subnets correct, and they are in the same workgroup. And the cables and network cards do not seem to be faulty, (emphasised by one machine being able to see the other one correctly)

Any ideas would be appreciated. Thanks.