>Can you use PC-100 and PC-133 ram in the same computer?
Yes, you should be able to. PC133 memory is downward compatible with PC100, PC66, and PC33 memory.
>How can you tell if the ram is PC-100 if there is no sticker on it?
A good memory ID guide can be found at http://www.dewassoc.com/performance/memory/how_to_id_pc133.htm
>… is there a specific arrangement when putting them in (biggest to smallest)?
No, but I usually put the largest one first. The largest memory I have is usually the newest and the break between modules won’t happen as often. That is, most of the time programs etc. will be using the first module.
If I had, say, a 256 MByte PC133 module, a 128 MByte PC100 memory module, and my computer supported PC133 memory, I would not install the PC100 module and run the bus a 133 MHZ instead of the 100 MHz required to support PC100 memory. It will run faster that way. I would guess that it would run faster with one 128 MByte PC133 module instead one 128 PC133 and 128 MByte PC100. Larry