Are you also buying DDR2 RAM? 'Cuz if all you've got now is DDR1, it won't work in the S3
The Dell OM3918 uses DDR2 ram, so that's OK.
BUT, it is probably DDR2-400. Newer boards don't show support for ram that slow. I've never tried it myself. Good catch!
What we want to see is DDR2-533.