This urge to build "programmers" seems to be a passion with some!! Its like trying to make a pen when you want to write.

For those trying to live dangerously by building thier own programmers :

Not all needed information to cover all possible variants are given out by many vendors - Atmel could be an exception. In my opinion to build a programmer you SHOULD have ACCESS to much more information than printed in basic data sheets.

Try developing code for your application and use a well tried out program for the "burning" part - this will atleast reduce the variables when you debug your application code - atleast you are sure there are no bugs to search in the programmer part.

Enjoy

Raghu