AVR-Chat

I'm trying to debug a line-powered AT90PWM3 (yay motors.  Code works 
*mostly*) application.  I need to go beyond "debug by printf", so I 
think I need to get another piece besides the STK500....

Can I use (I guess in order of preference, but correct me if I should 
prefer different ones):
  1. AVR JTAG/ICE/USB, at 
http://microcontrollershop.com/product_info.php?
cPath=110_161&products_id=938

It's isolated (so they say...), but can I use it in AVR Studio / IAR?

  2. A AVR Dragon (I'll build my own optoisolators) [digikey]
  3. JTAG ICE (mk 1) [fleabay]
  4. JTAG ICE mk II  [digikey]

I think I did something funny with the power sequencing, so when I 
changed compilers the board isn't coming up under IAR (works kinda on 
GCC, but the control loops aren't behaving right).