Matched pairs is usually the optimal situation especially with DDR. 80 bucks for 1GB (not megabyte im assuming) of DDR2 is a total ripoff.. get your memory online at places like newegg or directron and avoid the big chains like the plague.

Did they really sell you DDR1? If you need DDR2 and you have DDR1 it wouldn't even fit into the memory slot, the pins are different.

I am assuming you are running Windows XP x86. If so I'd shoot for 2GB, 2 1 gig sticks. Should be able to find that for 40 bucks or so. If your machine is been slowing to a crawl lately, I'd reinstall Windows as well. You will lose all data that you don't back up, but that's the breaks. It's just regular maintenance.

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1985 CA 300D Turbo , 213K mi