Vista Cannot Connect to XP

Hi

We have a home network with several XP desktops which can all see a
workgroup shared directory on one XP machine we use for general storage.
Recently we got some new laptops with Vista on them.

When we try to connect to the XP based shared folders we can see them in the
explorer but when we try to explore or map a drive we are asked for
username/password. All the XP based computers can connect with no problem but
the Vista ones all fail even when correct username/passwords are entered.

And yes we have turned on discovery etc and yes we have tried disabling all
Virus and firewall sw!! This is such a basic thing to want to do you would
think that MS would have got it right with Vista!!

Any assistance with solving this problem would be appreciated.