hmm..just think, though, your house would never be cold in the winter..;)
As for the memory, they change DIMMs like women's fashions. On some systems, you have to add memory in pairs, but considering you have 3 slots, that's not likely. The best thing to do is to add identical sizes, speeds, brands, etc. Also check with the mobo manufacturer to see what kind of memory it takes, what's recommended, etc.
I've seen all sorts of strangeness with memory. Here's a triva bit you probably don't hear about; some vendors say never mix gold-connectors with silver-colored connectors on different Dimms, they cause corrosion..;) what'll they think of next?..;)

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)