From http://bbs.thesims2.ea.com/community/bbs/messages.php?threadID=98bf9aa3ff5515a64a8dc6746bd6e36f&directoryID=225
EA response to question about specs for TS3
"Hello,
Thank you for contacting Electronic Arts.
It is hard to give an accurate answer right now, but be sure to choose a High-End computer. Your Computer must be at least a Core-2-Duo 2.0Ghz or higher, 2 or 4 GB RAM, a stand-alone graphics card with at least 512MB non-shared Memory by Ati or nVidia, never buy an on-board graphics card, to play the game. Of course game may need a lower or higher configuration than this, but this system is good for a ideal quality gaming experience.
If there is anything else we can help you with please let us know.
Thank you,
EARep Rick
EA Online Support"
EA response to question about specs for TS3
"Hello,
Thank you for contacting Electronic Arts.
It is hard to give an accurate answer right now, but be sure to choose a High-End computer. Your Computer must be at least a Core-2-Duo 2.0Ghz or higher, 2 or 4 GB RAM, a stand-alone graphics card with at least 512MB non-shared Memory by Ati or nVidia, never buy an on-board graphics card, to play the game. Of course game may need a lower or higher configuration than this, but this system is good for a ideal quality gaming experience.
If there is anything else we can help you with please let us know.
Thank you,
EARep Rick
EA Online Support"
They are referring to a system with Vista, as XP can only support (with modification) 3.5 GBs as issues arise at 3 GBS or higher with XP. On-Board Graphic Cards are the worse possible feature of any gaming rig. The only thing you'll need to upgrade is your graphics card, more so if you are using Vista as your ram will be drained.
In all honesty, Sims 3 is going to be popular because it is open, but at the same time the larger the city the worse the lag will become. It will be like playing a high-end MMORPG on dial-up with millions of people >.<