same problem here. WinXP pro machine, 1+Gb RAM.
Firewall running, antivirus not running.
I have the impression this started after one of MS security updates. Anyway, cmdagent.exe can use up to 100% of CPU, with continous disk access for a very long time, even when there is no other activity. And it also uses half or more of available RAM which apparently cannot be released/reallocated later. Result: the machine slooooooows down, freezes, sometimes picks up by itself, most of the times turns off randomly.
I will have to uninstall soon if I don't find a solution.