AVR-Chat

I'm very new to this, so I may not have things setup right but ...

I have a STK500 with a AT90S8515.  I would like to use PORTA for 
digital I/O.  I setup DDRA to 0xff (all output) and wrote 0xf0 to 
PORTA.  I got out my logic probe, and expected for half of the pins 
to be high, and the other half to be low.  What I found was that 
they behaved as if they were not connected.  I tested some known 
values, and so I know the logic probe is working.  I moved the whole 
thing to PORTC, and had the exact same problem.  Any suggestions???  
PORTB is already in use, and works.  I tried removing that portion 
of the circuit/program to isolate the problem, but it didn't help.  
It appears to be only with PORTA and PORTC.  I'm guessing there is 
something else to setup in order to "enable" PORT A/C, but I just 
can't figure it out.  Any help would be GREATLY appreciated.

Thanks,
dan