I have done a clean install of windowsXP on a P3 550 with 128MB ram. Without any other software installed the machine was using between 105MB and 115MB. that only leaves you about 15MB before your into the swap file. Personal option is 256MB just to do word processing and surf the web anything more and you need 512MB, I personally run with 640MB on my laptop (XP Home) and 1GB on desktop (XP Pro)