Installing memory

I attempted to upgrade a pc’s memory from 128mb SDram PC100 to 512mb PC133 SDram. The operating system is windows XP. I was told that the speeds PC100 and PC133 were interchangeable. Also the new memory is non parity. Does the non parity matter, I have researched some literature and cannot find this addressed. Is it the speed that is the problem? When I booted the machine up, the monitor would not give the display.