Win98SE slow performer in home network

I have a laptop running Win98SE and two desktops in a home
network. One desktop is running WinXP Pro and the other
Win2K Pro.

Immediately after I log onto the network from the laptop,
I can read and write files from the desktops with no
problem - nice and fast. If I keep the laptop on for an
hour or two and do the same thing later (through Windows
Explorer, for example), files are very slow to appear --
sometimes several minutes. They're equally slow to write,
and when I do, it sometimes report that too many files are
open or the save failed.

It sounds like a network issue ... any ideas on how to
keep things moving along? Thanks.