Can I mix/combine two Different Speed DDR400, 256mb and DDR333 512mb to my motherboard since my mother board supports this two speeds see at my signature on my pc spec. If I mix/combine this one is it possible that my memory run in DDR333(167MHz) and my RAM will become 768mb? as far as I know the previous SDRAM cannot mix/combine differrent speed like PC100 and PC133. Is there any problem in the Speed of my Processor?

there is no point mixing as the ddr 400 will run at the slower speed of ddr 333 so you wont get the xtra perofmrace of the ddr 400, but yes they will both work and your ram will increase to 768mb

OK it will run as youve said is there any problem with other parts in my pc mobo, processor etc. could it be no effect in the performance of my pc?

i dont understand what you mean by anything wrong?, but if you want to play recent games you would require a good graphics card, however i cannot reccomend one i dont really no much about graphics cards.

I mean is there any problem in my pc performance once I Combine this because I spend my pc recently in games, and home video editing

well it should increase performace because of the memory increase as long as your motherboard can take 768mb of ram, but both will run at ddr 333