I have a friend with a Dell pentium II 300mz. She wants to add 128 mb of ram but when I put in the ram new ram the comp wont start. (note the chip (pc 100 generic) works in my gateway pentium II 400mz) I have even tried putting in only the 128mb chip. There are 3 slots and 2 have 32mb chips in them. does anyone know it you need a different kind of ram (lower size, different speed) for this to work?

The memory depends on the system type. Is is a Dimension, Inspiron, etc.
A good link to look up compatable 3rd party memory is this one by Viking:
http://config.vikingcomponents.com/