I have looked at all the areas that have been suggested, and more. No joy.
XP - XP is fast on my home network - I have yet to try Win7 - Win7. Not sure I want to commit another PC to Win7 until the bugs are out!
Mike - speed and duplex are set to 100/Full on all devices. Interestingly the RFC for gigabit ethernet mandates auto-negotiation at both ends, for a proper implementation - fixing it is allowed, but does not handle errors and exceptions correctly.
Security is not an issue either, as I have (temporarily) disabled AV and any local firewalls for testing.
Homegroups
are not involved.
I have tried tweaking every parameter in NIC settings, no effect.
I have also looked at the version of SMB, but that hasn't made any difference either.
Oh well, just have to wait for MS to admit they have a bug (actually several) and fix it.
SD