...and if this machine is going to be used for any kind of heavy work, don't stop short of 1GB of RAM.
Biggest gain to productivity in office work is dual monitors. Some motherboards even come with dual VGA outputs now. Or get an ancient TI4200 card with dual outputs.
CPU is pretty immaterial on an office-type box, I'd just get the cheapest thing you can buy - but NOT a celeron.
Lots of RAM and big screens is what makes office boxes work well. Hell, Even a 1GHz Athlon would be fine.
17 inch CRT sucks donkey nuts for productivity because you can only get 1024 mode on them without eye-strain. Recommend dual 19" CRTs for high productivity. Seriously. I've run "dualhead" since early 1999. At work and at home I'm on dually 19" CRTs with 2560 x 960 screen resolution. Extra wide task bar spans two monitors - it rocks.
Just fixed up my GFs laptop at work, (today in fact!) so she has the laptop next to the desktop screen, and now has dual monitors. The Laptop at 1400 x 1050 and the CRT at 1280 x 1024 - but just the taskbar on the Laptop.
In just 4 hours use, she reckons her productivity is 10-15% higher. Ina week that'll be 20-25% easy.
19" CRTs like the Samsung 955NF are cheap as dirt now, and handle 1280 mode at 85Hz beuatifully. Remind your boss that 19" CRTs will survive at least one more round of computer upgrades, and that means 6 years from a sub-$200 monitor. At a pinch, settle for Viewsonic E95 or E90. They aren't "flat" but they are good.
Do *NOT* mix flat and curved surface monitors on dual screen setups.
Right now I'm staying away from my hometown (working) and I left the twin 19" CRTs at work, and brought along dual 17" Samsung 172X LCDs. YAY!
MOST IMPORTANT! The new nVidia drivers for dualhead absolutely suck a$$! Make sure you use 44.03 version number for drivers - otherwise you'll have real issues with productivity.
Entirely coincidentally, 44.03 is the fastest of all nVidia drivers and contains the famous "3dMark2001SE" "Optimisations". Funny that!