Minimum circuitry required to program an AVR
I have a page about a minimal board. The minimal circuit is the chip itself, and a couple of decoupling capacitors. A pull-up on /RESET is advisable (however the processor has a weak pull-up on it).



The six wires you mention are required for ICSP programming. An example from my page is:



That is using an Arduino as an ICSP programmer.

I think most designers would mandate the decoupling capacitors. You may get away without the pull-up on /RESET but probably at the expense of reliability.

The wires changed colour between the two photos because my earlier board (shown second) had the capacitors further away from the chip pins than they should have been. They really should be next to the chip for maximum effectiveness.



Note that, depending on the fuses, you may need to supply an external clock. In my case I did it like this:



The default chip fuses (from the manufacturer) does not require a crystal.