My computers home ( 2 vista and one xp ) work fine. I can access the shared documents on the xp desktop at anytime by just start-->run-->
\\192.168.X.X
Logging in remotely to the PC is not a problem either. I ran no setup wizards.
What service pack is the XP and Vista?
Are you trying to logon to the machine remotely or are you just trying to access some shared documents?