The best way to pair up RAM when installing it?

I have 2x256MB (PC originally came with) and 2x1GB (these are the new ones). I went on Crucial's website to scan my computer and it said my computer could hold up to 4GB of RAM (but i'm not gonna put that much in it). I'm a noob at this and need to know how to pair up the RAM. I have 4 slots available. Should I do it like this?

Option A)
Slot 1: 256MB
Slot 2: 256MB

Slot 3: 1GB
Slot 4: 1GB

Option B)
Slot 1: 256MB
Slot 2: 1GB

Slot 3: 256MB
Slot 4: 1GB

If you have an explanation to go with the option, i'd appreciate it :) THANK YOU!!!
 
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