I have a few questions...

What type games do you anticipate playing?
Are you looking for hardware advice or operating system advice?

I'll be honest... Gaming is a tough subject! Everything depends on how much you are willing to spend and what compromises you are willing to accept.

A top of the line gaming PC can run $4000(US) or more and play any game under the sun at the highest settings! It might even make coffee for all I know.

Luckily Sims usually don't require the horsepower that many of the action (FPS type) games need. I'm assuming you want to build your own, so I'll talk about some basic aspects and focus on reasonable performance without buying a $900 CPU (bang for the buck) and future upgrade ability...

OS: Windows 7 64bit. Gaming requires good video, but RAM is important for seamless play. You'll want 64bit so you can handle over 4GB if needed.
Case: Don't have to spend a lot here, maybe $40. As long as it has adequate places to ventilation and has the required places to put the drives and burners you want.
Power Supply: Not a lot to spend here either, $40 to $60. Look for a quality power supply around 600watts. Brands: Cooler Master, Coolmax, Raidmax, and OCZ are good brands.
Motherboard. Choose a brand with a reliable reputation and plenty of connections: SATA, USB, IDE. SATA and USB are more important that IDE. Make sure you choose a motherboard with the correct CPU socket for the CPU you want to use. ASUS, Foxconn, Intel, and Gigabyte are good brands.
CPU: I would go with a quad core in the LGA1156 i5 or i7 family for upgrade ability. (Get matching LGA motherboard socket). These CPU's start around $200 for an i5-750 and go over $1000. I'd shoot for an i7, maybe an i7-860 around $280. This is upgradeable, so if you need to shave cost you can go down to an i5 and still have decent performance.
RAM: The more you can afford the better. More RAM means less drive access which leads to a more fluid game experience. Also use the least amount of RAM sticks you can afford for the same amount of RAM. 2x2GB sticks are better than 4x1GB sticks. 4GB is a minimum and 6 or 8GB is better. If you go with the newer i5/i7 CPU you'll need DDR3 memory. Try to get DDR3-1333 as a good compromise. A 2GB DDR3-1333 stick runs about $60.
Video Card: Nvidia has been the gamer's choice in the past, but ATI has been coming on hard. Either will suit your needs. Look for the Nvidia GTS250 or ATI Radeon 5570 series with 1GB of onboard RAM. Direct X 10 support is mandatory. Direct X 11 support is preferred. You can find a reasonable card for $80 or go as far as $300.
Drives: 3.5" 7200RPM. Get 2, if you can afford it, so you can implement a good backup plan.
Fans: Get some big and quite case fans to keep everything cool!

The above info should lead to a reasonable system that plays Sims very well and will fly with everyday apps. It will also last for a long time. Of course CPU and memory are the most important of the components, but they are both easy to upgrade.

If you have less to spend bump the CPU down to an older quad cored like a Q8400(LGA775) and only run 4GB of RAM. This will limit future upgrades but will play games reasonably well.

If you have more to spend I would use an i7-860($280) and spend the remaining money on RAM and a better video card.

I hope that's the info you were looking for!

No problem, David. Is that the information you were looking for?

I didn't know what your budget is so it's general info, but everything is a compromise. If your budget is less you can always make adjustments.