The System idle process is exactly what it says, idle processor time that not been allocated/used by anything so that pretty much normal.
If you go to your start menu, then RUN type in MSCONFIF and it will bring up a configuration menu, go to services and tick the button that say "HIDE ALL MICROSOFT PROCESSES" you will then be left with a list of Misc processes, see if there is anything abnormall there, if so then you can simply stop it from booting with your pc by untick the box.
If usure just untick them all (ensure all the microsoft ones are hidden first!!!!!) and then save and re-boot, any service that is need that has been turned off will automatically start when its needed, if this process that cusing you all the CPU strain is not part of windows then you should be able to prevent it from taking everything up by doing this.
Give it a go and let us know if that solved the problem