I have used a little utility called whatcpu for a variety of times where I need to know the CPU that's in a box. www.datadepo.com
I have not used the sysid mentioned above but it does look interesting and will have to try it.
I might also suggest that you take a look at TRACKIT from www.blueocean.com. It includes the ability to inventory your computers, the components AND the installed software, (often overlooked aspect) and create a database that assists during the upgrade decisions and future tracking of what is where etc. I have recommended this for several companies and they have really gotten alot of use out of it.
If your going to be making a upgrade plan then I would strongly suggest that you plan to visit each machine and make additional evaluations regarding retention (if any), conditions of monitors, additional devices attached, specialty software and requirements, and general placement.
I have worked in numerous organizations where Desktops are made into towers for deskspace, where unknown software is installed BUT MUST be retained, (and doesnt run on anything but old equipement without upgrade to package, and where additional connections are in place that must be accounted for. Walking it one time and taking notes saved alot of future trips and tripups.
HTH