Lower user's (not process') priority

[Root Of All Evil]

I have (sole) root access on a Sun 4/110, OS 4.0.1 .
Other people sometimes use my machine, but when i want to run
a CPU or i/o intensive program while other people are doing
stuff, i want to be able to claim lots of time.
Furthermore, I want to be able to do little things while other
people are running their intensive programs.
It is inconvenient to go find out the PID for a program,
log in as su, and renice it.
I would like to be able to renice *all* processses from
user TrivialPerson to about 19 or 20, and make mine all
about -19 or -20.
Can this be done?
How?
Thanks,
Tony Zador