CLiu: While I am no expert on the subject, I think you should be able to use this memory, subject to the caveats below. Mixing different memory speeds and sizes generally just results in giving you the lowest common denominator in terms of memory speed and timings. You should still be able to overclock, but here is the caveat. You have taken a 100MHz bus processor and set the bus to 138. Your PC2700 memory is capable of 166MHz, so that's not a problem. The PC2100 memory is only rated to do 133MHz. So, it may or may not stretch to 138 MHz. It probably will, but you never know. Also, with a voltage adjustment and good cooling they say your processor often can get to 2.4GHz on a 150MHz bus, but the PC2100 memory probably won't make it there.
I don't know anything about your motherboard. I think that board has a ratio setting to set the ratio of the speed at which the memory operates as compared to the bus speed. If not, then if the motherboard does not have a memory speed setting the memory would be operating at the bus speed (technically double the bus speed).
This is just my understanding and I am no expert. If someone has a better understanding please chime in. I'm an Athlon man myself.