I have a similar issue, and thought I would share my findings.
One Vista Computer, One XP computer.
Gigabit NICs, Netgear Gigabit Switch.
The XP computer has two shares -- one large, one small. Both shared are the
entire remote volume on the XP system.
The Vista computer has one share, and used to run XP. When it ran XP there
were no performance issues.
All systems register as being on the same "Local Network" for security groups.
File transfers from:
Vista --> XP Small share - 4-6 MB/sec
Vista --> XP Large share - 700KB/sec
Vista <-- XP Small share - 10 MB/sec
Vista <-- XP Large share - 10 MB/sec
Now, I remote desktop into the XP system, and try the same tests.
XP Large share --> Vista - 11 MB/sec
XP Small share --> Vista - 11 MB/sec
XP Large share <-- Vista - 25 MB/sec
XP Small share <-- Vista - 25 MB/sec
I then set up the IIS FTP server on the XP system, and tried some file
transfers.
Vista --> XP 40 MB/sec
Vista <-- XP 7 MB/sec
I repeated all of the above tests using a crossover cable (to make sure the
switch wasn't the problem) and got similar results. I also repeated the
above tests with identical results with a second NIC.
When trying the same tests with my XP laptop and the XP system, through the
same switch, I max out the 100Mb inteface on the laptop.
With this information, I called Microsoft support, spent a few days on hold,
and got brushed off.
My guess, is that it is something to do with CIFS and security settings. I
have tried various changes in netsh, and gotten nowhere. I also marched
through the services list disabling one at a time, and didn't get anywhere
either. I haven't tried changing the services one at a time and rebooting
between each change. That might be my next attempt.
I might also try WireShark, and see if I can see anything unusual in the
network traffic.
My guess is that once the corporate customers start complaining, Microsoft
will issue a fix. For the time being, I'm stuck with FTP.
If anyone else has compared FTP vs CIFS speeds in a similar test, I would be
interested in the results.