Windows XP Memory

Having problem running your windows Vista in your old PC?Just like before when windows XP first came and people facing system run very slow in 128 RAM, and now when you Vista installed on 512 RAM it will run very slow. Do you know that when installed in 128 RAM, the OS it's self need 100 MB RAM, for the word processing,spreadsheet, pdf reader each application need 20 MB RAM. And if you run internet browser, you will need 50 MB RAM. That is way for windows XP batter to use 256 RAM rather then use 128 RAM.