Geforce 6600 Pro 256mb got QE/CI but some Apps will crash....

I have installed Leopard 10.5.1 for AMD v1 and installed the natit.kext ,everything works out of the box except that Camino will lag behind very slowly when I scroll some web pages, especially when pages are full of flashes or QuickTime movies and sometimes it will crash if I scroll too fast, so does Firefox and Opera.Safari will do a better job,but it would hug the CUP when I load some pages full of movies etc.QuickLookServer consumes a lot CPU when I use coverflows and QuickLook.

I just wander,if I really get QE/CI and even can watch movies,play Google Earth,how it would behave so strangely? I look around google but nope.Can somone here tell me what is the problem? Have I need to do some tweaks to make it works perfectly? What is the biggest trouble maker?-- java? my card ? or my my poor CPU?

Thanx in advance!

MY Spec:
Sempron 2800+ Socket 754
ASUS K8N4E-SE
AC 97 Audio,Realteck 8139 LAN
ELSA GeForce Gladiac 6600 Pro
Identifiant du périphérique : 0x0141
Identifiant de révision : 0x00a2
RAM 512*3 @ 200MHz
HDD: IDE Seagate 80G + 250 G + SATA 160G