Hmm, that's more or less my testing technique, apart from occasionally (every half hour or so) going back to the space lane for a spot ofThere is a reliable way to reproduce the crash: Launch, witchspace and then leave the computer alone.
Plus, even with debug=yes (aka a simple 'make') I'm sure the frame rate I'm getting on the xp computer is much higher than 4 fps. This with a 1.6 GHz processor & 2 gb ram. I'm not there now, but I'll double check the fps the moment I have the chance, though.
I might be totally wrong here, but my initial guess is that whatever causes your computer to be so slow with the debug exe is also causing the crashes. Not being there is kind of difficult to guess properly, though...