They switched the screenshot key to one of the letter keys in NL v1.5 as default. All the functions are assignable however in the NL options screen. If you're really in trouble, press H while in simulation mode and that will show you the current key assignments.
EDIT: I opened up no limits and checked the default settings. K is the screenshot key if you haven't changed your assignments. *** Edited 10/13/2004 2:56:27 AM UTC by SFWoARules!***