No, it won't work.  The R300 requires Registered ECC DIMM's.  The one you listed is Fully-Buffered (FB-DIMM's), which would not even fit in the slots. www.kingston.com/.../search www.crucial.com/.../listparts.aspx
I'm asking If Kingston DDR2/667 4GB ECC CL5 DIMM Dual Rank x4 (KVR667D2D4F5/4G) is compatible with my PowerEdge R200 can anyone answer this?
PowerEdge R300 memory