In order to stop Cydia from crashing on your iPhone or iPod Touch, you'll need an iPhone or iPod with firmware 3.1.1, 3.1, 3.0.1, or 3.0, SSH installed both in your computer and in your device. Now first SSH your device into your computer and navigate to /var/lib/dpkg/updates. Delete the files named as 0000, 0001, 0002 and so on. Now your Cydia should work fine. If that doesn't work, try reinstalling Cydia on your iPhone or iPod Touch, as it could be a different problem.