Win7 boxes suddenly refuses to recognise XP boxes on the LAN

If I believe what I read about Windows 8, it's more infuriating than Win7. So far, though, Win7 provides enough frustration for a lifetime. The requirement here is that four Windows boxes on this home LAN, two running XP and two running Win7, see each other's drives and folders with full control and without passwords. Effectively, they comprise a single integrated workspace. Last year,...