Pc133 or pc100 won't work. Pc2100, pc2700 or pc3200 will work, depending on your motherboard chipset . It must be 184 pins. Some folks still use the term ddr sdram, which is confusing.
Since the size is 256MB, you may be correct and what the OP identified as SDRAM might actually be DDR. It's easier when part numbers are provided.