2.6.19-rc6-git12 fails in exactly the same way, from /var/log/messages it seems 2.6.19-rc6 19/11/06 first saw the problem, details later when I boot 2.6.19-rc5...same problem with 2.6.20-rc3. Last worked with 2.6.19-rc6-git12, so it was 2.6.19 where it failed.
Attaching both case1 normal, case2 acpi=noirq. With acpi=noirq ethernet doesn't get configured, route -n says it's an Unsupported operation, ifconfig only shows for localhost, ifconfig eth0 192.168.10.5 also complains of a config error.
It seems that the "acpi=noirq" (and probably also the acpi=off) case
is simply an additional broken case, not a success case to compare to.
The thing we really want to compare is dmesg and /proc/interrupts
from 2.6.19-rc6-git12, and the broken current release.
Perhaps you can put that info in the bug report when you file it.
thanks,
-Len