Many MIDI Rules users (including me) have/had troubles with system freezes and MIDI crashes of the BCD2000 while using MIDI Rules and Traktor. Both issues have to do with real-time performance of your system (OS, hardware, peripheral devices, applications, etc.). One bottleneck component is enough to slow down the whole system.
Therefore optimizing the system performance has to cover all involved components. Windows XP users should take a look at the Windows XP Optimization Guide. A lot of tips can also be found in the NI forum. If you know additional tweaks/tips, please comment.