Why is the Sims 2 Bon Voyage running so slowly?

The booklet tells me to turn off the backround tasks, I did and it still take like 15 min to load my house or a business or downtown (i have all of the EPs except pets and seasons) My computer is a decent speed. either 512 or 1024 RAM, both are good enough to run it smoothly. It doesn't have a virus, it was just recently fixed because of a virus, the memory was wiped. It have a HUGE amount of memory left on it, the is like nothing on it. Oh and its Windows XP home edition if that matters.