Sims 2 on new computer + DH going nuts adding houses & sims = choppy play?

We got a new computer at the end of Sept. - it has 2G SDRAM and an 80G hard drive I think... I bought it for multimedia, not gaming though. We decided to get The Sims 2 and now my husband has gone nuts building houses and a gazillion Sims. Now our game runs terribly - choppy and slow. What can we do to fix this? Is there an overwriting problem? We also added Family Fun Stuff and Glamour Life Stuff packs.