Can I put DDR 300 Ram surrounded by a motherboard that have a DDR400 slot? If so, how can I, and what do I necessitate?

Thanks!!

Can I put DDR 300 Ram surrounded by a motherboard that have a DDR400 slot? If so, how can I, and what do I necessitate?

Yes. DDR333 and DDR266 memory can dance in DDR400 slots. They adjectives use the same 184-pin DIMM form factor, and any motherboard that can support DDR400 can support the slower DDR speeds.
Yes you can, freshly open the element, put it in the memory slot, next reboot. All you need is a screw driver to unscrew the crust.
Yes, installs the same opening as DDR400.