Memory Problem
If you are using WinXP you should really have at least 256 megs of RAM , ideally 512megs (seems to be the "sweet" amount for XP), although many people including myself have much more than 512.
Here's What You Need to Use Windows XP Home Edition
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
The above are the Microsoft requirements, they are always very conservative as to not to exclude wood be consumers.
So if you are able to afford it I would get at least 256 megs of RAM