I am having a HP Pavilion 6716 laptop. It came with Windows XP. I installed Vista and found it as slow. I contacted HP and asked for ram upgrades. But they were too slow to response. As per system specification I ordered a 2GB stick of RAM. It is a regular DDR2 PC2-5300 RAM. And it is compatible with the laptop. After adding the RAM in the system the system simply failed to boot. There is a bit difference between both the ram models. But I think that can ignored. The old one is 533Mhz and new one is 667Mhz. So does that can cause any kind of problem. Thanks.