DDR2 vs. DDR

what is the difference and does ddr2 fit in mobo's as does ddr.. example my mobo ..lol.... nf7-s v2.0 ? also what would be best ram speed to buy im looking at pc3500 cause realluy i dont think i can get my barton (locked) that high anyways ... unless i bought some mobile but will mobiles easily reach fsb of 433 if i have good psu and using my mobo that i have ? aslo what is the so called best "mobile" to buy for overclocking ?

thanks ya'll

2500 or 2600 mobile best ocers, DDR2 is 240 pin ram, DDR is 180(i think) and no your mobo doesnt support it, just read the pqi thread on some good ram to get