The tech who told you that putting a PC133 stick in a PC66 bus is "taxing the RAM" is full of horse pucky, and has no idea what he is talking about.
To give you an idea of what nonsense he is spouting, imagine this:
You go into a tire store. You ask to have new tires put on your car. The tire salesman tells you, "Don't put THOSE tires on your car! Those tires are rated to go 200 miles an hour. You only drive 55 miles an hour. Driving at 55 miles an hour taxes those tires. They will fly apart."
It is not "taxing" to go SLOWER than what you're rated to go! "PC133" means "Certified to work at any speed up to 133MHz, but not faster than 133 MHz."
The old chips did not work in the G3 because the memory controller in a G3 can not work with "high density" DIMMs. "High density" DIMMs are the ones that store a lot of memory on just a few chips.
There are two kinds of DIMMs in wide circulation: normal and high density. the only difference? High density have fewer chips on the board (4 chips instead of 8), and each chip holds more information.
The beige G3 was invented before high density chips existed. It sees 4 chips on the board and says "Aha, this must be a 64MB DIMM, because there is no such thing as a 128MB DIMM that only has 4 chips."
