Slowing down a dual-core WinXP machine?

I’m stuck at work right now trying to debug a pretty complex piece of Flash code. (It’s an XML-driven Flash scripting engine, basically.) It’s not my code, and it’s got timing bugs that mean that some of the people testing it in our office – on relatively slow Macbooks – are seeing bugs that I don’t see on my development machine. Which, needless to say, makes it fucking hard to fix this crap.

What I want is a way to play back the movie artificially slowly. Or, failing that, to slow down my system to enhance the odds of seeing these timing bugs.

What’s the best way to bog down a dual core WinXP machine? Bonus points for freeware. Does 3DMark 2006 or whatever actually load up both cores? Are there prime number testers etc etc. that can max out a multicore machine? Hell, are there any plain old CPU throttlers that can seriously, seriously underclock a modern box (Dell Optiplex)? Lay 'em on me and I will be most grateful.

I think switching off all caches in the BIOS might slow down things, but I dunno if that would be enough.

This might help: RightMark CPU Clock Utility

CPU Burn-In

Freeware, small, easy to use. This will only load your CPU at 50%, you will have to run another instance of the program to bring it up to 100%.

StressPrime

This is the program I use for CPU stability tests. It will also run RAM + CPU mixed stress tests. This will load both your cores at 100%. Make sure you grab the duel core version of the program though.