Robert,

Are you planning on using a Philips or Atmel RD2?
I wrote ISP routines for the Atmel RD2. The routines are very easy and straight forward. I did find one problem. I had to place the routines in the lower 32K of memory. The same routine in upper memory would not execute correctly. One nice thing about the Atmel RD2 is you can overwrite your ISP routine while executing it. Of course the routine and location of the routine cannot change.
I required the use of an emulator to debug my ISP routines. I don’t know of any emulators that support all the functionally of the flash but MetaLink makes one that will support everything except the physical write to memory. This emulator was very useful to me.

Michael