I bought my Presario s6000z (Athlon XP 2600 / mATX) before I became aware of modding and the possibility of having a silent PC. In the process of researching how to quiet this thing down (it's my main entertainment PC), I discovered that the CPU is running at ~50 idle, ~70+ under stress (e.g. playing games).

In addition to the lobotomized mainboard (supposedly an Asus A7V8X-LA, though the BIOS is from AMI), I've got some fairly heavy-duty hardware in there, including an Audigy 2ZS-Platinum and an Arctic Cooled Radeon 9800 Pro.

I've had no serious problems with this setup, and everything seems to be running stable, but I would like to see if I could improve the CPU cooling with a secondary goal of quieting the system.

I'd love to thrown in a Zalman 7000, but looking at the mobo I'm not sure it will fit. The current heatsink about 65mm x 82mm, with 22mm-tall capacitors very close to the sides (the 82mm width). From photos and descriptions I don't know that anything I've seen will fit this space -- maybe the taller/narrower setups like the Scythe?

The CPU fan also has mainboard-controlled (I think?) speed settings; the fan kicks in when the temperature hits about 72 Celsius. I presume that without any tweakable BIOS settings that I can't change this... will that affect my ability to put in an aftermarket cooler? Do aftermarket coolers have connectors that will report properly to the mainboard?

I just realized this is a very long post... since I'm a total n00b I can't tell what information I need to describe and what I can skip. I appreciate any suggestions or help anyone might have for me!!!

@70C+ you're running close to a crash & loosing your top score! My XP2200 cops out @88C on the nose. Presumably you done all the obvious stuff like cablegami & opening up fangrills etc?

Can't really advise about your hardware as I'm not that familiar with it.
However, Prune your StartUP programs etc to the absolute minimum to avoid any uneccessary CPU load. A good place to start is running processes, which you can find under Task Manager. You can quickly identify any you're not sure about via one of several websites devoted to this subject such as:
http://www.processlibrary.com/

You'll also find some helpful Software on the downloads page for checking your temps etc:
http://www.silentpcreview.com/Web_Links+index-req-viewlink-cid-19.html

Motherboard Monitor is good 'cos it gives you a great high/low display, sadly I don't think it's under development any more.
IF? you can get Speedfan to work (dunno about Mobo compatibility) then you will be able to control your fans in Windows & hopefully run them at a minimum. A search in the forums will give you tons of hits on these.

Best of luck!

There is no need to put down the temperature as long as your setup ist stable. In order to save energy during idle, have a look at http://forums.silentpcreview.com/viewtopic.php?t=20903

Thanks to both of you. Yes, the system is running stable, so it's not exactly an "emergency" to get this thing modded. The fact that the CPU fan only kicks into high speed around 72 C is a bit weird, but there's nothing I can do about it.

The motherboard is totally lobotomized -- I can make no voltage or underclocking changes, AFAIK. No one's been able to overclock it, so I assume I can't underclock it either.

I'd still like to cool the CPU down further and reduce case noise with an aftermarket CPU heatsink / fan. Like I said in the original post, the problem is that the motherboard is so squeezed for space. The new heatsink can be no more than 65mm x 82mm and be able to clear 22mm-tall capacitors on the 82mm side.

I realized maybe this is the wrong forum... should I repost in the CPU Cooling forum?

My guess (and this is just a guess) is that the motherboard's BIOS instructs the motherboard to supply a full 12V to the fan when the CPU temperature is above 72 degC. When the CPU temp is below 72 degC, less voltage is supplied.

If you have a spare fan with a 3-pin connector and also a 3-pin/4-pin converter, here is something you may try. First, take the Presario's CPU fan and plug it into a "normal" power connector with the 3-pin/4-pin converter. This is to make sure the CPU fan keeps running. Next, take another fan with a 3-pin connector (like an old CPU fan) and connect it to the CPU_FAN header. (Do not bother attaching this spare fan to anything. The only purpose of this exercise is to make sure that aftermarket fans will actually work at all on this motherboard.)

Now turn the computer on. If the computer boots up normally, then you should be OK installing an aftermarket fan.

By the way, does the computer show any sort of data about the CPU fan's RPM?

I don't know about the "total n00b" part. From the questions you are asking, it sounds like you have a pretty good idea of what is going on.