I also have a core 2 duo 2.83 Ghz processor....
Lol...so i dontcare how much avast takes,,,

but i need to tell my past exp of the time when I had a 1.7Ghz with 512 Mb Ram. Avast was of some help in those dreaded virus world...

I tried with NOD32 too...its also a good silent AV. may be norton and other stuffs are good too..
but best thing about avast is that it offers this all services for free (Home Edition)..So why not use legal sw rather than cr@cking something paid like Norton or NOD32..
As my exp goes NOD32 cr@cked version doesnt stay valid for longtime as the illlegal copies are identified easily..
so better use free version rather than comprising on the PC's security.