Hey anybody! Please, I need hel.?

In my PC, I've got 741-M motherboard. It accommodates 2 184-pin slots and it supports DDR400/333/266 SDRAM. I've got 1Gb (2x512) of RAM (PC2700). I would like to upgrade my computer to 2Gb. But, when looking for RAMs on the Internet, online shops offer differen types of memory, including DDR, DDR2, DIMM, SIMM, etc. And also SDRAM. So, which type of it I need to get? DDR or SDRAM? Are they the same or different?