Registered DDR memory are only usable on Socket940 AMD64 MoBo. So, unless you buy an Opteron or an Athlon FX for Socket940 you don'T need to wrry or bother about Registered DDR memory. Socket 754 and 939 use "normal" DDR memory.
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A7N8X / <font color=green><b>AMD Sempron 2800+</b></font color=green>
Kingston DDR333 2x256Megs
<font color=red>Radeon 8500 128Megs</font color=red> @ C:275/M:290