I have an MSI K7N2 Delta-ILSR board which I know can take up to three 1G sticks of PC3200/2700/2100/1600 DDR SDRAMs. These can be 64-bit or 128-bit.
However MSI state that the board will not accept x4 1G memory, but will accept x8 or x16.
Although I have scoured this and other forums I cannot find a clear description/definition of exactly what "x4" is referring to and how I can tell, from it's specification, whether a particular memory module fits the bill.
Virtually any unbuffered memory you buy these days will be x8 or x16. And technically, those with 16 ICs (double sided with 8 on each side) will probably 2 banks of x8 ranks ie double sided. The spex of the RAM should be given by the maker, designating x4, x8, or x16.
IMO, you should select brand name of the RAM you want and check with that manufacturer to get a list of RAM they have certified with your board.