I'd go for SDRAM. I haven't heard of RDRAM though found this:
Yours would definetly support SDRAM as this is the standard.
I think RDRAM is for electronic devices and bigger workstations so I doubt your motherboard would support it.
Hope this helps
So yeah SDRAM is the way to go. Make sure though you get the bus speed which your motherboard will support. mine for example will go to a max of 3200 speed DDR SDRAM. Some motherboards will allow higher than this, so its best to check before buying.