Just a guess, but it looks like you computer takes DDRAM (like the Samsung stick) and your 1Gb stick is just DRAM. There is no way the 1Gb would show up as 512 if it was the correct memory.
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My Fault, I put DRR in the first post for the 1GB stick but what I really meant to put was DDR.
try taking out the ram and putting it back in pushing hard