File Transfer through router problem

I have 3 Computers networked using a
Linksys BEFSR41 v2 Wired Cable Router (firmware:1.45.7)

All 3 access the internet at blazing speeds.

Computer 1 transfers files to and from
to computer 2 or 3 at REALLY Slow rates.

But Computer 2 or 3 can transfers files to and from
each other at FAST Speeds.

The Router is 4 years old, all the CAT 5 cables are New
and have been tested individual..
Computer 1 is brand new ( I just built it )

The Network Port on Computer 1 is built into the ASUS Motherboard
its a Marvell Yukon 88E8053 PCI-E Gigabit Ethernet Controller

Computer 2 & 3 both use SOHOware 10/100 PCI Network Adapter Card


Is the problem the Router ? or the Network built into the Motherboard ?

Thanks,
Mod edit - we do not respond by email on a one to one basis - all problems are dealt with on the BBS for the benefit of all. Email address removed for security (your security) reasons.

 

Have you tried swapping around ports on the linksys?

To rule out the linksys hook all the PCs to a switch and connect the switch to the linksys,

 

All Fixed

It was the Network Speed/Duplex setting (on my new motherboard)
I had it set to 100Mbps, but had to change it to auto-sense