Process Tamer is a tiny and super efficient utility for Microsoft Windows XP/2K/NT/Vista that runs in your system tray and constantly monitors the cpu usage of other processes. When it sees a process that is overloading your cpu, it reduces the priority of that process temporarily, until its cpu usage returns to a reasonable level.
Version 2 has the same ultra-efficient minimal engine, but tons of improvements, including a nice gui configuration tool, lots of customization options (for example to disable the balloon tips), changing icon for easier identification, optional logging, a quick manual priority changer, and more.
Tools and Utilities
Product page: here