Leopard freeze

[pcgame]

Hi everyone, i've a problem. Occasionally when i use any apps or i download some file leo freeze and i must reboot.
Leo hangs with forefox after 10/15 sec
Can you help me?
I trying boot leo with this flags: cpus=2(or 1) platform=x86pc(or ACPI) but nothing

My pc
AMD x2 3800+ @ 2.5Ghz
Abit An8 sli chipset nforce4
Nvidia 6600 gt 128 mb
2x1 Gb Kingston

P.S.If the English ago penalty I'm sorry, but I'm Italian