Cut-Copy/Paste behavior (selecting should not put in copy buffer)

I know that this subject has been discussed to death, however, it is by far 
the biggest productivity killer for my work.  Every day there are dozens of 
tasks I must do which involve copying or cutting text and pasting into 
another spot or another application where it needs to *replace* existing 
content.

I use RH8 and I have been told that the Linux/Unix standard is that 
highlighting content automatically puts in into the paste buffer whether I 
like or not and that there is nothing that I can do about it.

As for 3-button mouses, I did not know that they still existed outside 
museums, thus I am not sure if I could switch to one or not.  (Or if it 
would help.)