Hmmm, i posted this before somewhere... *digs old reply out*
okay, have one sweeper with EQ/surf. attach the amulet coin to that sweeper and put it in your first party slot. For EXP, attach the EXP. share to the pokemon you want to train and put that in your second party slot.
Next, go battle Gabby and Ty, the reporters who circulate around the region. now use your sweeper against them. If all goes well, you should faint them both on the first turn, you will get twice the money from amulet coin, and your pokemon you trained with the EXP. share will recieve 3/4 of the EXP. points. this is the easiest solution. You can battle them infinetly this way.
NOTE: if you use earthquake (EQ) as your sweeping move, make sure the weak pokemon knows protect so it doesn't harm it.