I am wondering whether an idle computer and one running seti draw the
same amount of power.  

No.  I have a graph of power consumption as measured by the UPS
attached to two systems (sampled every 10 minutes).  You can easily
spot when it has problems sending back work units or getting more.
If it sampled more often, you could probably tell when each work
unit finished. (downloading a work unit takes a lot less CPU than
processing one).  Since the two systems have different power
characteristics, I can also tell which system finished a work unit.

I suspect I would be able to see the same info in a graph of CPU
temperature if I tried collecting that info.

The power difference for the system between idle and 100% CPU seems
to be about 15% of the power used by the system (including hard disk,
CD-ROM drive, RAM, keyboard, motherboard, etc., but not the monitor).
Obviously the difference in power consumed by the CPU itself is much
larger.  And every system will come up with different numbers.

Also, can you notice if seti is running while
you go about doing your daily routines on your pc?  

No.  SETI is running at "idle priority" and everything else takes
precedence over it.  (Note, however, that I'm not running Windows).

					Gordon L. Burditt