You need to expose the CPU temps on your network, which will require running some dedicated software on each PC by either setting up a script that can query the CPU temp and then publish it or installing specific software such as Core Temp (http://www.alcpu.com/CoreTemp/) which can do this, though you may need to write your own Add On. Your Pi would then need to poll each of your published end-points to gather the data.
You could also access existing software on the machine remotely from the Pi. For windows this would be a remote call to
wmic, which can be done from nix via python. (http://www.tomsitpro.com/articles/issue-wmi-queries-from-linux,1-3436.html)