XP Home/Vista network

I am trying to set up file sharing between an XP Home PC and a Vista laptop.
The PC can see files on the laptop. The laptop can see the PC, but when I
click on the PC, I get the following error:

\\XP_DESKTOP is not accessible. You might not have permission to use this
network resource. Contact the administrator of this server to find out if
you have access permissions.

Access is denied.

As far as I know, all permissions are set to allow access both ways. Any
help would be greatly appreciated.

Thanks.