well btc uses sha-256 as an algo
and ltc uses scrypt as an algo.

the difference is that ltc/scrypt is appr. 1000x slower. So instead of 100mhashes u get 100khashes. now while btc is optimized for gpu and fpga right now, and asics anytime soon, ltc was optimized for cpu and gpu. with my mining rig i get about 600mhashes mining btc and 750 khashes mining ltc