RAM question, for the geeks here

Sooo, one of my 512 blocks died on me a few months back, and I’ve grown reeeally irritated on my PC’s slow performance due to that.

What exactly should I be looking for when upgrading RAM? I’ve no clue what all the techs are on blocks nowadays (SD, DDR etc), and also no clue what the “PC3200”, “PC4800” etc means…

I’ve got an Athlon64 3200+ running XP, what on EARTH would you recommend? I’m going for a 2Gb solution, either 1x2, or 2x1…