Computer gets really hot under Linux

When I'm in Linux, even just idling, I can hear the fans of my Pentium 4 (yes, it's a shitty processor, but that isn't the point) working overtime to where they sound like a vacuum.

The only time it does this in Windows is when I have Oblivion or SimCity 4 running for about an hour.

I even have my Linux kernel dynamically-throttle my CPU speed such that Linux only turns up the frequency when a program is running that needs more computing power (I believe this is the CPUFreq series of settings in the kernel setup), and even when the cpufreq is a mere 400mhz, the fans are spinning as if the CPU is going at full 3.2ghz.

What can I do to prevent Linux from making my computer into a sauna-creation machine all the time?

In before "delete Linux and your shitty Pentium 4"

Yes, the problem is that linux follows ACPI specs very striclty, which Windows does not. And a number of BIOSes don't either and are thus technically flawed. Now if you boot a linux kernel on one of those BIOSes, many strange things can happen.

You can try updating your BIOS or get fixed ACPI tables for the time being. And with a little luck, a workaround for your board/bios may get put into the kernel in some time.