Kernel does not boot without noapic or maxcpus=1

Binary package hint: linux-source-2.6.15

I have just installed Ubuntu 6.06 LTS amd64 on an ASUS M2N-E motherboard with an Athlon 64 X2 4200+ processor. When booting the computer (either the installation cdrom or the installation on the hard drive), bootup hangs right after the kernel startup, after the following lines (when quiet and splash boot options have been disabled):

Begin: Running /scripts/init-premount ...
[ 47.410739] ACPI: Fan [FAN] (on)
[ 47.414595] ACPI: Thermal Zone [THRM] (40 C)

The computer boots normally if I define either noapic or maxcpus=1. However, with noapic my USB keyboard stops working after a few minutes with the following error in /var/log/syslog:

Aug 29 22:40:48 kleinbus kernel: [ 512.290816] irq 7: nobody cared (try booting with the "irqpoll" option)
Aug 29 22:40:48 kleinbus kernel: [ 512.290821]
Aug 29 22:40:48 kleinbus kernel: [ 512.290822] Call Trace: <IRQ> <ffffffff801689f5>{__report_bad_irq+53} <ffffffff80168c6a>{note_interrupt+538}
Aug 29 22:40:48 kleinbus kernel: [ 512.290843] <ffffffff880a888a>{:usbcore:usb_hcd_irq+42} <ffffffff80168357>{__do_IRQ+215}
Aug 29 22:40:48 kleinbus kernel: [ 512.290867] <ffffffff8011302f>{do_IRQ+47} <ffffffff80110460>{ret_from_intr+0}
Aug 29 22:40:48 kleinbus kernel: [ 512.290876] <EOI> <ffffffff80315870>{thread_return+0} <ffffffff803158c2>{thread_return+82}
Aug 29 22:40:48 kleinbus kernel: [ 512.290885] <ffffffff80315e6d>{preempt_schedule_irq+93} <ffffffff8010e6e0>{default_idle+0}
Aug 29 22:40:48 kleinbus kernel: [ 512.290894] <ffffffff8010e718>{default_idle+56} <ffffffff8010e806>{cpu_idle+150}
Aug 29 22:40:48 kleinbus kernel: [ 512.290902] <ffffffff8012032d>{start_secondary+1261}

If I follow the advice and set the irqpoll option, I get a kernel panic right away.

The kernel version the above output and dmidecode have been acquired against is:

Aug 29 22:26:53 kleinbus kernel: [ 0.000000] Linux version 2.6.15-26-amd64-k8 (buildd@king) (gcc version 4.0.3 (Ubuntu 4.0.3-1ubuntu5)) #1 SMP PREEMPT Thu Aug 3 03:11:38 UTC 2006

I'll add dmidecode output right away.