In my humble opinion Vista from XP is a backward step. To keep using XP, use Firefox instead of Internet Explorer and keep your antivirus up to date.
Why do I think Vista is a backward step. It will run slower on the same hardware. If you do install Vista, once set up and updated, about three days, do not switch off, only put to sleep, will help make it a little more useable. When Vista starts it checks for updates, TrustedInstaller, is the process running and this can take up to 15 mins to complete and in the mean time the computer is quite unresponsive.
As for the RAM sticks, they won't fit W8 laptop but may fit older machines. Run Crucial scanner to see exactly what is installed and compare with is available.