Rokins, Most ram will work fine together just fine if its the same major speed/type (cant mix ddr2 with ddr3). Kits are sold for practical reasons, most people want to fill up their 2 or 3 channels and buy 2-3 sticks anyway so why not sell them in pairs/triples? But do open up your computer and buy something that is as similar as possible in terms of brand, speed, looks etc, doesnt hurt to be on the safe side but you should absolutely not have to discard your sticks and buy three new ones.