4GB RAM installed, 2GB showing?

I have Windows XP SP 3 32-bit . I just bought 2x1GB memory sticks for my pc, plugged em in and System Information or systemrequirementslab.com are not showing 4GB, but 2GB RAM as before. CPU Z and System Tools however show 4GB . CPU Z shows all slots used and 1GB each. System tools says 4GB physical memory but virtual still 2GB. My Computer-View system info> shows 2 GB, shud be 3.4 or something? Help?