Vista<>XP network copying speed

I've got the same problem as is being reported all over the 'net.
Peer-2-Peer network, Three XP-SP2 machines and 1 Vista machine. All
connected wired thru a SMC router/hub at 100M connection.

In all cases, Xp<>XP file copies is as quick as I'd expect on a 100mb lan,
however, Vista<>XP is dirt slow - always less than 10bps usually about 5.

I've tried all the suggestions on the net I can find:
- netsh command
- mapping network drives
- turning off Ipv6
- turning off Remote Differential Compression

Also, tried 3 different routers (The SMC, an older DLink and a brand new
Gigabit Dlink) all had the same problem.

I have tried the latest drivers I could find for my onboard RealTek 8139
NIC. Also no improvement.

Has Microsoft acknowledged this problem at least?
Rob