[CentOS] System freeze on laptop: power saving daemon doing harm?

Hi,

I have CentOS 4.3 installed on my Fujitsu Siemens Amilo D laptop
(Pentium IV 2.4 GHz CPU). Everything runs just fine, but I have one
problem. When I leave the machine unattended for something like an hour
or two, my desktop has "frozen". Unable to recovery anything, even
[Ctrl] + [Alt] + [Backspace] refuses to quit X, so I have to hard-reboot
by pressing PowerOn/Off for 10 seconds. 

First thing I did after install, I deactivated the XScreensaver because
it kept asking me for a password everytime I stopped typing for 5
minutes. 

There must be some other power-saving daemon there that makes the mess,
but I don't know much about these. I've heard somewhere that ACPI can
cause system crashes... but I don't know where to even start to look.

As far as I reckon, I have an ACPI daemon running, a thing called
'irqbalance' (that produces a nice red 'FAILED' on every shutdown) and
also lm_sensors. 

Any suggestions?

Niki Kovacs