8GB RAM not showing up in system properties.

The issue im having is i just bought 8GB (2x4) sticks of DDR2 800mhz PC6400 and i've installed them and it comes up in the motherboard BIOS as 2gb in each slot and a total of 8192MB. Now the issue is that when i right click My Computer - Properties it only shows that i have 3.25GB but when i go into system information it says i have Total Physical Memory of 8,192.00 MB. I go to this website that i use to see if my PC can handle the games or not and its saying i have exactly the same amount of ram i had before i put the 8Gb in saying 3.25gb. I have Windows XP 32 bit SP 3. I did a diagnostic from the motherboard and the RAM passed the test so and its showing it some places but some not. anyone got any tips? Thank you in advance.