[Technic] Need Help Figuring Memory Swaps

[Denise Ash]

Trying to get my workstations to 1 GB........

Which number here is the speed?  What do I have to match to match the speed.

DDR2 PC2-4200  DDR2-533 is what I can buy now - 512 MB Stick

The machine has DDR2 PC2-4200U-444 - 1 512 MB Stick

Do I match the 4200 or the 533 and 444?  If I can't match the 444 
then I have to go to just a 1 GB stick right.

I am trying to use some of the existing memory I have.

Thanks
Denise