cmshn :
you have altered all my thoughts.. giving up intel and start using amd is something i've never thought about..
i dont think buying ddr3 because i have already have 1x4 ddr2 and it seems enough but i'm not sure what i should do..
amd seems logical i'll think about it.
thank you very much..
and i have one more question..
if my motherboard is suitable for quad i'll only buy a processor.
but as i said i have 4 gb ram and i says 3.25gb i'm using windows7 x64.
is it because of my motherboard?
my mainboard is biostar 945p a7a i i'm not wrong
3.25gb is because you are running 32bit windows it can only use a total amount of 4 gigs and that includes the memory on your video card.
So you want to use your DDR2 ram which is not a problem so in that case go AMD will be a better system and cheaper and also you will still be open to upgrade paths in the future with AMD as for 775 Intel is dead socket.
ASRock A785GXH/128M AM3/AM2+/AM2 AMD 785G
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157180
AMD Phenom II X4 965 Black Edition Deneb 3.4GHz 4 x 512KB L2 Cache 6MB L3 Cache
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103727
This setup will allow you to reuse your DDR2 ram and leave money to spare which I suggest getting a really good video card An HD 5770 would be a great choice of video cards but thats another thread.
This is a link for benchmarks that show the Phenom II 965BE beating the Q9400 in everything.
http://www.anandtech.com/bench/Product/76?vs=102