I believe your motherboard requires that you run it in dual channel mode. You have to use two sticks of the same size. Get another stick of 1GB memory (preferably from the same manufacturer). My friend has an HP that is the same way. He has to use two stick of the same size.
Good luck,
Shane Davenport
Update: I just looked up your motherboard and as I suspected it requires the memory to run in dual channel.