hmm, now i read up on this a bit more it appears it is not possible to program serially after the reset pin has been disabled.
i missed this in the datasheet the first time round:
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while
RESET is pulled to GND.
so it appears the reset pin must be low WHILE the AVR is programmed.
i initially thought that it could be programmed AFTER a reset (which i was planning to do in software).
back to the drawing board.
need to find a way to multiplex 2 inputs.
or build myself a parallel programmer.
or maybe an AVR with more I/O pins.