Can somebody please explain the difference between active and passive pickups? cuz im buying an LTD ESP EC-1000 and it has the 81/60 EMG active combo... and I just wanna know why some artists such as alexi laiho and the dude from lamb of god preffer the passives?

Actives have a higher output therefor are better for distortion, and less good for cleans than a good passive. You can still play cleans better on them than crappy passive ones though, just as in the same way some people prefer passive pick ups for distortion. They prefer the tone, it's just all personal preference. EMG's are darn good pickups whatever though.
Hoodoo you do Mr. Bellamy