XP Pro file sharing (SMB) performance problem

Archived from groups: microsoft.public.windowsxp.perform_maintain (More info?)

I recently installed XP Pro (SP2) on a PC I have been using for running
a few server applications (it previously had a trial edition of Win2K
advanced server on it, but I didn't fancy paying for it when the trial
ran out!). The machine is a PII-350 with 128Mb of RAM, so I've cut
down the services that run on startup as far as possible, and have it
sitting at about 100Mb RAM usage (of which some is generally swapped
out, so there's ~40Mb of cache). Most things are running OK (as far as
can be expected for a machine that's so close to the OS's minimum
spec), but I'm getting absolutely terrible file sharing performance.

I have a directory with a number of .avi files that I used to watch
from my laptop over a wireless network (802.11g, infrastructure with a
belkin router and cards -- PCMCIA in the laptop and PCI in the server,
typically getting about 48Mbit/s connections) both machines are
connected to.

With Win2K this worked fine, but with XP the files open very slowly and
the frame rate drops well below the correct level. Looking at what's
going on with the 'performance' applet in Control Panel/Administrative
Tools, the throughput is abysmal -- typically about 13K per second.
Some applications manage to get a faster throughput, e.g. if I copy the
file to my local disk before viewing it, I get up to about 100K per
second, so there's no fundamental limit that means the system *can't*
do better than that -- it just won't when I'm trying to watch the
video.

I've tried a few registry hacks I've collected in various places over
the Internet: I've disabled last access updating, I've increased the
SMB command buffer size, I've upgraded the lanman server thread
priority to 15 (real time). I've switched the performance options to
optimise for background servers, and for system cache. All this has
had some effect, maybe increasing performance by about 20% -- but I
need to increase it by at least 50% to make this system useful.

Any ideas what might be going wrong?

Jules