A working way to share with Vista etc. ?

What would be the best way to set up the local network so that
machines can share files and printers with each other?

There is an ADSL-modem/DHCP-server/router/firewall and a wireless hot-spot
connected to it. (Kind of radio extension of the LAN.)

There is an old Windows2000 SP4 desktop that acts as "the server":
Printers are connected to it, and it's used for "central storage" so that most
of the files to be accessed from all machines are kept in its disks.
This machine has no WLAN, so it needs to be connected via cable.

There is also a Windows7 basic laptop connected via WLAN.

There is a Vista desktop connected via WLAN.

There is a Vista laptop connected sometimes via cable, sometimes via WLAN.

All operating systems are 32-bit. The Vistas are SP2.

The problem:

Between the other machines the default workgroup and simple file and printer
sharing works fine, but with the Windows7 laptop there are problems:
Sometimes the other machines in the LAN aro found, sometimes not.
Internet is always accessible, but the resources on other machines sometimes are
and sometimes are not.

The disappearing of the other machines from Windows7 "network-folder" doesn't
seem to be dependent from time or anything. It looks quite random.
After boot, everything is seen. Then you surf in the net foe a while, and 2 machines
have disappeared. Later all the other machines, icluding the hotspot and the
ADSL-modem are disappeared, mut the internet still works fine.

If I open the "file damager" and try to open a shared directory on the Win2000
machine by typing ""\\WIN2KPC\shareddir" in the address-bar it sometimes opens,
sometimes opens when given the username/password, and sometimes
just gives an error message (no chance of giving any username/password),
that windows cannot access the target (sorry, poor translation from Finnish)
with error code 0x80004005.

You never know if you can or cannot access the shared directories.
And that's most irritating.
I guess due to just one Windows 7 machine, home network is out of question.

How to stop the Windows 7 machine from "loosing" the other machines in the network?
What could possibly cause the problem?

The UAC was turned to level zero, but it doesn't help.

Newest Malwarebytes hasn't found anything.

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