I've got a Sparkfun ATmega8u2 break out board that I think I trashed the DFU bootloader so I got out my STK500 and opened the programmer in AVR Studio 5.1 added the STK500 plug-in and looked at the list of devices. No ATmega8U2. So I opened AVR Studio 4.0, opened the programmer and it went right to the STK500 and has the ATmega8U2 in the list and opened it and read the signature and fuse bits.
So, WTF? Does this mean I have to get an STK600 to use AVR Studio 5.1 with the ATmega USB chips? I'm not willing to pony up for one if it is only the off chance that I can make AVR Studio 5.1 work.