Samba issues on busy network

[stan]

I have a Ubuntu machine that I use as a VirtuakBox host for an XP instance.
The XP instance puts it's data files on a Samba share on a remote machine.
The task running on XP is a data collection one, and runs continuously.

Now that I have put this in production, every morning, when I come in and
check it, this task is complaining about "disk" problems. I am almost
certain that the problem is caused, when my Amanda backups run, in the
middle of the night. During this time, the network traffic on this subnet
gets quite high. The VirtuakBox host, and the Samba machine are on the same
switch, and subnet.

Any ideas what I can tweak to try to make this better?

-- 
One of the main causes of the fall of the roman empire was that, lacking
zero, they had no way to indicate successful termination of their C
programs.