I was wondering: If the default internal 1MHz RC oscillator fuse setting was left intact AND a 8MHz crystal w/ 2 caps (of proper value) was put across XTAL1/XTAL2...would you see the proper (crystal) frequency signal on XTAL2? I realize the AVR would operate on the internal 1MHz clock.
I looked in the datasheet (used mega8 as an example) and I could only find block diagrams, no schematics (of course that doesn't mean they are not there...I just didn't see them). I just now thought about looking in Sleep sections...I will go look now.
I only have a STK500/501 and there isn't really a way to (easily) connect a crystal and caps directly to an AVR, otherwise I would test this for myself.
My apologies if this turns out to be in the datasheet somewhere. I spent 10 or 15 minutes browsing around.