Ram Wont Fit?

I picked up some ram on e-bay for my ibook g3 500 mhz i checked out the specs and it said SO-Dimm and that s what the ibook is supposed to take but when i went to install it it didn't fit. the lil notch wasn't lining up right, Idon't know what is wrong so what ram is the right kind?

revision: I think i know why- is there a differnce between pc-100 so-dimm and pc2100? Because in the item description i just noticed that it says the ram is pc2100, i don't know if this was a typo or this is an actual type of ram.

pc2100 is DDR memory, your computer takes SDRAM which is in speeds PC100/PC133, so they are different sizes

http://www.crucial.com/store/listparts.asp?mfr=Apple&model=iBook+(G3+500MHz)&tabid=AM

That is the ram you need for your system