The Atmel STK600 starter kit can be used to house Atmel AVR devices to which the AVR ONE! can connect through the JTAG interface.
When connecting to a JTAG target, simply use the 10-pin 100mil stand-off adapter (provided) to connect to the JTAG connector on the STK600.
When connecting to a PDI, debugWIRE, or SPI target, simply use the 6-pin 100mil stand-off adapter (provided) to connect to the SPI/PDI connector.