Have you check the Manufactures website to see if the modules have been tested as OK.
PC5300 DDR II RAM (DDR-667) NANYA NT2GT64U8HB0JY-3C 2GB appears to be listed at the only 2GB module that is supported, that's not to say that newer modules will not work that have just not been tested.
Looking at the list of modules http://www.msi.com/file/test_report/TR10_265.pdf There are not listed 800mhz Modules that are 2GB in size.
Though the motherboard supports 8GB of memory it probably won't work unless its the 667 Memory.
In fact the website for this board states the following
Main Memory
• Supports four unbuffered DIMM of 1.8 Volt DDRII DRAM • Supports up to 8GB memory size (DDRII 533/667). • Supports up to 4GB memory size (DDRII 800). • Supports dual channel DDRII memory architecture. • Supports DDRII 533/667/800 memory interface.
http://www.msi.com/product/mb/P965_Neo.html#hero-specification