The Sims 2 does NOT run smoothly on my mac. I have the newer MacBook aluminum with the 9400M chipset and that game can barely run 800x600 on low detail on the Mac side. However, on my Windows side it runs full-detail without ever really dropping below 30fps. I had all the expansions installed through Apartment Life, and I uninstalled it because it was simply unplayable.
I would just invest in getting it for Windows, if you have a Boot Camp/Parallels/VMware setup, and just using that. It'll likely save you a lot of hassle as I haven't seen a patch yet that addresses the horrible job EA's distributor did translating DirectX into mac-friendly OpenGL.