Home Network with Vista and XP Strange Behaviour

Hi,

I have read and re-read the posts about vista-xp networking but somehow the
suggestions still don't work. I can access the Vista laptop through the
desktop PC XP SP2 which is wired to the router but I can't acces the desktop
pc via the laptop which is connected wirelessly, though it shows it in the
"Network" window. I get an error that says Windows cannot access (computer
name) error code:0x80070035 network path was not found. Then it offers to
diagnose and then when it has finished, it says "Cannot communicate with
(Computer name) 192.168.1.3" This seems strange as I can access Vista with XP
but not XP with Vista. Can anyone help please? Thanks.