2500+ AXDA2500DKV4D = 1833MHz Barton (Model 10) 333FSB (166.6 x 11), 512K cache, 1.65V, 85ºC Max Die Temp
Ok the XP2500 runs at 1.833. If it is showing up as XP1900 then you need to go into bios and look for the place to adjust the Front Side Bus Speeds to 166mhz.
TYhe graphics problem you may want to try and disable any anti virus program as they sometimes cause problem's. Where did you get the Nvidia drivers from?
click here is the place to get them, look for the 53.03 WHQL certified ones