I use a D-Link Router to connect 3 computers within a home network. I
use Bandwidth Monitor Pro to monitor network activity. However, I
can't figure out a way to monitor just the internet activity that the
system conducts (which is pretty much limited to the computer that has
the monitoring program installed) rather than (what I have to date)
all network activity i.e. I routinely transfer large volumes of data
between computers within my house; this transfer showing up in
cumulative data transfer summaries.

Any suggestions/ideas as how to set this up? After much 'fiddling', I
suspect that the program I'm using will not allow this.