Need new ram badly!

Well my computer is a compaq presario never upgraded it in my life and i think it's about time to upgrade. Currently it has 256 DDr SDRAM memory

my computer uses DDR RAM.Maximum total memory you can upgrade up to 1024 MB. My computer contains 2 DDR-DIMM slots for PC 2100 DDR-DIMMS. the maximum memory my computer can place module size is 512 MB in one slot.

Help me pick out a new one.. Maybe around 500mb

i need it cheap as possible..

http://www.newegg.com/Product/Product.asp?Item=N82E16820220005
http://www.newegg.com/Product/Product.asp?Item=N82E16820141215

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