Can an Xbee accept 5v communication signals from an Arduino without frying, or do I need to step them down to 3.3V?
The actual XBee chipset is 3.3V but depending on what you are using your board may accept 5V. You really need to read the specs on whatever you plan to use. To answer your question: If you put 5V to a 3.3V system you are likely to damage it.