Mac Pro early 2009 8-core : freezing problem

Hi.
My keyboard and my mouse freeze every 2 sec during half a sec and then start working again. So every 2 sec, i've got to wait until they start responding again. I've contacted AppleCare and for the second time, they're replacing my Mac Pro. So I'd like to know if there's a known problem with this computer or if I'm in a run of bad luck and the third one will be the good one.
I've tried by the way with multiple keyboards/mices (corded and cordless), under Leopard given with my Mac Pro and with a retail DVD. I've also tried reinitialising the PRAM (as told by AppleCare). I've also installed Windows on another hard drive and curiously, keyboard and mouse work just perfectly without any freezing. I hope I gave you enough details and sorry if my english is not perfect by I'm French!
Regards.

Mac Pro 8-core 2.26 GHz
6 GB RAM
640 GB HDD
AMD HD 4870

I suspect you have a software problem of sorts, or a problem with the hard drive that OS X is installed on. The fact that it doesn't happen in Windows which you have installed on a separate hard drive pretty much eliminates the remaining system hardware.

When you receive your third Mac Pro, instead of loading it up with all your software and whatever else, just run it with a bare copy of Leopard installed to see what happens.

Regards.

I've tried Leopard and Snow Leopard beta on another hard drive too. Same problem...

Still very strange that Windows runs OK with no freezing and you have it installed on a separate hard drive.... I don't think it's a hardware problem but I guess you'll have to wait and see when your third Mac Pro arrives.

Regards.

Yeah I know. With all the things I've tried, it's neither software nor hardware... Guess I'll have to wait. Thanks anyway !

Well I've found what I was looking for by my own:
Apple - Support - Discussions - Keyboard/Mouse freezing on New Mac Pro ...

The AMD HD 4870 dosen't work (yet) with every DVI monitor...

Good find. Glad you finally got it resolved. Too bad you couldn't keep all those Mac Pros at the same time.

Regards.

Yeah too bad!

I sent back my Mac Pro and ask for a refund to buy the "standard one" with the GT 120. I'll also take the eVGA GTX 285 hopping it'll be better, but apparently Apple/eVGA drivers for OS X are still not "so good", as the 285 gets beat in some tasks by the old-gen HD 3870...

Review: NVIDIA GTX 285 on an 8-core Mac Pro - Ars Technica

Thanks anyway for your help!

Regards.