Which Memory You Guys Think I Shoud Go Get?
I Have Right Now In My Pc Ddr2 4200 533 Mhz (dule 512x2)

My Friends Told Me Get Ocz Or Corsair?
Should I Get Dule Channel?
And How Fast I Can Go In Buying Memory On Memory Speed (up To 800mhz? Or 650mhz?)

Thanks

memory model type and speed are selected as per motherboard specification...

You need to know which one is compatible with your motherboard...

read on your motherboard manual
most of the times mixed memory types are not supported and even if they are supported not recommended
because if you have 2 types of memory then you will get speed of slowest memory available no matter what is the speed of other memory....

going for some other type of memory is only recommended if you are replacing your current memory with new one

to increase memory simply take same type of memory and you may choose any brand in my view all are equal..