FPS is lower in crossfire than other games

When i play crossfire, my fps is like 50-55 fps with no fps lag and then suddenly for some reason i dont why, my fps just goes all the way down to 10-15 fps and then it seems like im playing the game frame by frame and then after like 10 seconds it goes back to 50-55fps?? what the heck??,my laptop specs are:
Processor:Intel Pentium M Processor 1.74Ghz
RAM:2038MB(2GB)DDR2
Direct X :10.0
OS:Windows XP SP2
Graphics card:Mobile Intel 915GM/GMS,910GML Express(128.0MB)

are these specs good enough to play crossfire with no fps lag? because if i can play it with 55 fps at one point that means that my computer can handle it but, i dont know why its going down suddenly and then going back up.I tried restarting my laptop,i tried playing crossfire when my laptop is cool and not hot,i tried upgrading directx,i used game booster,i tried shutting down some services but, it still happens,an ideas are welcome.please help i really wanna play crossfire with no fps lag.Thank you for your time