You seem to be aiming very high with the graphics card, especially it's onboard RAM, yet the CPU itself as a 3200XP is comparatively entry level. Seems an odd combination to me.
How about an alternative approach to speccing the system. Look at prebuilt systems from the likes of Mesh, Evesham, Dell
, and even some of the smaller perhaps more specialist suppliers like poweroid, overclockers, etc. Have a look at the specifications offered for the money. That gives you a clue about the basic balance of a system. Once you have that then you can start to look at tweaking individual components to suit your "specialist" needs. i.e. smaller HD (you can always add another later on) might give you money for more RAM or a better DVD drive now.
If SIMS 2 is anything like SimCity in it''s demands it is infact not so much about a big powered graphics card as the PC itself having sufficient power and memory to handle the increasing data of your ever larger simulation. But if you are building a gaming PC, you don't want to be one game specific. It wants to be balanced for all you can throw at it. Today I'd aim at at least an Athlon 4000+ chip socket 939 type (higher if I had the money), 1GB PC3200 RAM (again can always be easily added to later), SATA hard disks (access time is noticeably faster - ask the clan how quickly I'm usually ready to go on the next maps in COD), and a reasonable graphics card, but a 128MB onboard RAM on something like a 9800 card could be failry well balance for that sort of system.
I'm comforably running MOH, COD and now Battlefield 2 on a system that has slightly lesser specs than that. Move much higher and your into cutting edge and thus high priced technology that your current gaming expectations will not really show value for money.