If it's honestly 38° centigrade in your room then I'm not surprised that it's running so hot, even on idle. The P4 is an awful processor and I regret having purchased mine, multimedia be damned!
If you're still concerned with the temperature and you've done all the things you've claimed to do then the only alternative that I can think of is getting
a new, heavy duty, heat sink. There are plenty of third-party ones deploying fancy techniques like
heat pipes.