Memory Question - outcome of exceeding the memory limits of a machine.

This may be just a stupid question, but I've never seen it asked before and
I don't know the answer. I realize this is a forsale forum, but I can't
figure out where else to ask it, and I figure there are probably several
memory experts.

I have an emachine (etower 667ir) that I bought used, and it has the ability
of handling up to a total of 256mb (PC100 SDRAM) within two slots. It
currently has one128mb stick, and I wanted to expand the memory to the max
of it's limit by adding a second 128mb stick. This was when I starting
thinking about my question.

My question is what would be the most likely case if I was to place two
256mb PC100 SDRAM sticks (total of 512mb) inside the machine, exceeding the
256mb limit.

Would the computer:
1.  just not work and freeze, or
2. just access the first 128mb in each stick, or
3. just access the first 256mb in the first stick and ignore the second, or
4. nobody knows because it's unpredictable?

Anyway, it was just a thought, since a person can over clock a some
machines, it just seems a bit logical to be able to exceed the memory limits
to a degree.

Thanks
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