I did not follow the whole thread, but have a few remarks:

- this is perhaps the crappiest type of switch I know (and I think it is the cheapest at the same time). Disassembly it and look at how is it designed. Please have a look at your local electronics shop, you'll certainly find better. Or, better, consider using a jumper.

- AFAIK the autobaud in the 'RD2 allows almost any reasonable frequency crystal if you use low enough baudrate (2400-9600) for the ISP (this is so with the Philips' - I am not sure with the Atmel variety but IIRC it is similar). You might have troubles with the Dallas variety, though, as they specifically check for certain frequency/baudrate combinations only - but this is reasonably well documented in their datasheets and appnotes.

- I've thought about building a "switchable crystal oscillator" from a PLL - they can be dug out from old 386-486 motherboards, but only some of them provide frequencies interesting enough for a '51. Of course, there are PLLs of other types around, but this seems to be simple, available, and cheap enough for playing.

JW