i've loaded two different programs onto two different chips. the problem is that now they are stuck on the chips with no way of getting to the bootloader

I, Fortunately, do not know Atmel. I do, however, have a guess based on my Philips knowledge.

The chips arrive in ISP mode and thus the only thing known by programming first time is that the serial comm is working. Thus, if the first attempt fails, your problem must be with that.

For following programmings the "kick into ISP" must work as well.

I suggest you find the Atmel version of my NoTouch that someone published and include it. At least for Philips, it is a buttsaver and, in addition, makes life a whole lot easier.

Of course once Philips introduced the 'V' seriaed NoTouch became a lot less important.

Erik