Although it is not a good idea to mix memory, especially from different manufacturers, you might be better off just biting the bullet and get a new 4 GB kit. Although there are others that will tell you everything will be fine. Sometimes it works, sometimes it doesn't. Just make sure whatever you get is compatible with your motherboard or system. You can search memory manufacturer websites using their RAM configurator program. Most want to know the motherboard, but some will accept the pre-built model number instead. It will then show all compatible memory that they make for your motherboard/system. Long-winded answer I know (lol), but I hope it helps.