I currently running Debian Lenny on my D945GCLF with last kernel, but the problem seems to be the same.
So, my conclusion => bug with kacpid, due to r8101 or r8169 modules.
In fact, with my Netgear GA3131 card (r8169), or with the onboard r8101 chip, the system freezes when become idle.
If something is running, like "ping www", no freeze. When nothing is running, the system freezes in 1 or 2 minutes.
Last weekend, I turned off the onboard chip, and only use another PCI card with Marvell chip.
Result : no freeze at all in 4 days (24/24 7/7) ... unbelievable !
I currently running Debian Lenny on my D945GCLF with last kernel, but the problem seems to be the same.
So, my conclusion => bug with kacpid, due to r8101 or r8169 modules.
In fact, with my Netgear GA3131 card (r8169), or with the onboard r8101 chip, the system freezes when become idle.
If something is running, like "ping www", no freeze. When nothing is running, the system freezes in 1 or 2 minutes.
Last weekend, I turned off the onboard chip, and only use another PCI card with Marvell chip.
Result : no freeze at all in 4 days (24/24 7/7) ... unbelievable !
If someone can confirm this with Ubuntu 8.04.1.