drr sodimm, will this work in my computer?

 
     
   
I have a dell latitude d800, was wondering if the product above is sufficient for it. also, can I add just one of these and place it next to an already existing 512 card? or do I need to buy two of the same as both are probably running at different speeds?


To take advantage of the DDR both sticks should be identicle


 
     
 

drr sodimm, will this work in my computer?