I bought my TX2500z with 3GB. I would like to upgrade to 4GB (and vista 64bit) to take advantage of the Dual Channel feature and make the notebook a bit more efficient. I am planning on getting another 2GB stick and replacing the 1GB I currently have. However, do I need to get the exact same brand as the one I currently have? Or, does it work in dual channel as long as it matches (i.e both being PC2-6400)? I hope my question is clear.