What are some solutions to these causes of a slow LAN?
RAM in workstations.
CPU in workstations.
Increase in number of nodes.
Increase in traffic and loading.
Upgrades in applications (i.e., upgrade in Windows)
New applications (i.e., access to Internet).
Increase in graphics use.
Configuration problems.

Well, there could be a few things. First I would let everyone know
what kind of hardware you're running both on your PC's, as well as
your network, my guess is its probably a combo of decently bad network
hardware coupled with either bandwidth utilization or just slow
computers themselves. Too bad i cant submit a real answer :P

I think your network type (Ethernet, IPX, Fast Ethernet), your
bandwidth, the topology of your network (Bus, star, etc) and the
network Hardware like Hubs, Switchs, Routers, Firewalls, etc.  Also
the Native Operating System (NOS).

a link to How Ethernet works:
http://computer.howstuffworks.com/ethernet.htm

I hope it helps.
Phossil.

You've already listed quite a good collection.
These days the processing power of a node (CPU/RAM) hasn't 
kept up with the enormous growth of bandwidth. So the slowness
of a typical LAN (100 Mb)cannot be contributed to any networking
part (like the links themselves or the switches or routers --
these are really really fast and even running at a fraction of
their capacity can bring down a node).

So the slowness experienced is totally an end system issue.
Either the software/application running is slow. The node has
less RAM or a slower CPU.
Usually even a faster CPU can be less responsive, if there are
tons of junk processes running. So try to clean up the machine of
unwanted application (which are a HOG on CPU plus RAM).

Once you get the CPU load down and with tons of free RAM, the
network performance will be good. This low load of CPU/RAM should
be ensured in the other end of the communicating node too.

A simple way is use two linux nodes with minimal apps and test
a ftp like programs performance. See if you hit CPU usage 100%. 
Then its easy to isolate the bottleneck.. CPU or RAM or network.

Karthik

Karthik