The Sims 3 is 100% compatible with Windows 7. If you can't run it, it's because your system doesn't meet the requirements.
Windows 7 and Vista users (all versions of 7 and Vista)
• Windows 7 (all flavors) or Windows Vista (Service Pack 1)
• 2.4 GHz P4 processor or equivalent
• 1.5 GB RAM
• At least 6.5 GB of hard drive space with at least 1 GB additional space for custom content
• 128 MB Video Card with support for Pixel Shader 2.0
Also if you go to www.canirunit.com you can test your computer to see if you meet the minimum and the recommended requirements.
Windows 7 and Vista users (all versions of 7 and Vista)
• Windows 7 (all flavors) or Windows Vista (Service Pack 1)
• 2.4 GHz P4 processor or equivalent
• 1.5 GB RAM
• At least 6.5 GB of hard drive space with at least 1 GB additional space for custom content
• 128 MB Video Card with support for Pixel Shader 2.0
Also if you go to www.canirunit.com you can test your computer to see if you meet the minimum and the recommended requirements.