Ok manan, you are outta luck! You won't get PC2100 (= DDR266, which happens to be your RAM) in the market now. The only ones you get easily are DDR400 (PC3200). You gotta hunt for DDR266 RAM. Its better you sell the old one and get 512MB x 2 DDR400 to run in dual channel mode. Its not recommended to mix RAM of 2 differnt freqs and timings. It may or may not work after mixing. Hence be sure and get new RAM and don't use the old stick.