Re: memory upgrade
To run in dual channel mode, two modules must be the same capacity, and run at the same speed and timings.
Most motherboards have two channels. These two channels would usually be: DIMM 1 & 3 and DIMM 2 & 4, although sometimes it will be 1 & 2 and 3 & 4. Put the two 128MB sticks in first channel (1&3), and put the two 512MB sticks in the second channel (2&4). That way all your memory will be running in dual channel mode.
AMD Phenom II X4 955 BE @ 4.0GHz + TU120E lapped - MSI 770-CD45 AM3 - 2x2GB OCZ DDR3 1333MHz - Sapphire HD 4870 - Samsung Spinpoint 500GB 7200RPM 16MB cache HDD - Tagan TG600-BZ Piperock - (Currently open test bed) - Windows Vista Home Premium 64bit.