You may remember the paper released by a princeton research group regarding cold boot attacks on notebook computers in order to recover crypto keys. click to view old blog entry
The princeton research group has now released the sourcecode of a tool which will be able to recover the key, providing that the key is still stored in the DRAM. This can be achieved by severly cooling down the DRAMS temperature.
Turning off pxe or overall network boot may get you some valuable time, but its probably best too look out for ninjas who are carrying major cooling devices. Apparently they look something like this: