256MB of RAM meets the requirements. But in my personal opinion i would not run XP on 256MB of ram. But yes thats enough technically but again i love to run programmes such as Adobe Photoshop CS so i like lots of RAM.
To install Windows XP 'Home' (or 'Pro' Edition) onto your new PC, it will need to meet the following specification:
PC with 300 megahertz (MHz) or higher processor clock speed recommended; 233-MHz minimum required;
(Intel Pentium/Celeron family, AMD K6/Athlon/Duron family, or compatible processor recommended)
128 megabytes (MB) of RAM or higher recommended
(64 MB minimum supported; may limit performance and some features)
1.5 Gigabyte (GB) of available hard disk space
Super VGA (800 × 600) or higher resolution video adapter and monitor
CD-ROM or DVD drive
Keyboard and Microsoft Mouse or compatible pointing device