I have a working rt2500. Do you have a properly set up access point which is known to work with other wireless systems? Should the ESSID be set?
Still, it shouldn't crash. The serialmonkey driver seems to be updated almost daily. Are you using the latest version?
I think you would have a better chance of good advice on the forum for this driver at
One thing you could try is to delete/move the config file in /etc/Wireless if it is there, and just using iwconfig.