Short mouse and kb pause every 2 secs, any ideas, Really annoying, no idea what is

I've managed to install Leopard 10.5.7 on my PC, specs below. The installation appears to have worked fine, except that whilst using it I get a very short (>1 sec) pause every ~2 seconds! It is as periodic as clockwork. The mouse jumps around and the keyboard stops typing.

This is NOT a system hang. If I run Safari with a flash animation then it keeps going uninterrupted whilst the mouse dies. The pause appears to only affect the mouse and keyboard (that I've found). I've tried unplugging all other USB devices and I've tried another mouse, all with the same effect.

Activity monitor shows nothing using CPU or Disk during the spikes. dmesg reports that an NTFS partition on my drive can't be mounted, but only once. It shouldn't be this should it?

I've tried booting with cpus=1 to disable the second core. The disable takes effect, but it doesn't fix the problem.

Any ideas as to what can cause this, or at least how I can go about debugging it?

Specs:
Intel Core 2 Duo 6800
Gigabyte GA-965P-DS4 mobo
ATI Radeon 4870
4GB RAM
1 SATA-attached drive - 2 partitions (Primary: Mac file system, Secondary: NTFS storage)
1 SATA DVDWriter

Thanks very much, this is driving me mad!.kLink { display: none; } .iAs { display: none;}