If you want to know if Vista and the Sims 2 are compatible it would be worthwhile to visit the official site. They have whole pages devoted to FAQ regarding the Sims 2 and Vista. This is basically what they say:
"Thinking about upgrading to Windows Vista or getting a new Vista machine? We've been extensively testing Vista with a wide range of hardware and came up with this handy guide.
Q: Is The Sims 2 compatible with Windows Vista?
A: Yes! The Sims 2 and its expansion packs run well on Windows Vista. If there is a problem, it's mostly likely due to the Vista support of your graphics card. (See more details below).
Q: Will my computer be capable of running The Sims 2 on Windows Vista?
A: The required hardware for The Sims 2 on Vista is a 1.3GHz processor with 512MB of memory. The extra memory is needed is because 512MB is required for a Windows Vista Capable machine. Since Vista does use up more processor power, game performance will not be as good as on an equivalent XP machine.
Q: Ok, I've got that. What about my graphics card?
A: This is where it gets tricky. Because of new graphical features, Vista requires a DirectX9 capable graphics card. Here's a rough guide of graphics card capability:
These cards will fully support DirectX 9 and should provide the best The Sims 2(and Vista) experience
ATI Radeon 9800 and above. (9800, X550, X600, X700, X800, X850, X1600, X1800, X1900, X1950)
NVidia 6000 series and above. (6600, 7300, 7600, 7800, 7900, 7950, 8800)
These are early DirectX 9 cards and budget cards that may not support all The Sims 2 graphical features.
ATI Radeon 9600, 9700, X300, X1300
NVidia 6200, 7100
Unsupported cards in Vista:
These cards aren't DirectX 9 compatible and may actually work fine, but are not Vista capable. As a result, graphics card manufacturers are unlikely to support Vista driver updates for these cards.
NVidia FX5000 series (FX5200, FX5600, FX5900, FX5950) and earlier (GeForce 3, GeForce 2)
ATI Radeon 9500 and earlier, including 7000 and 8000 series
Q: Hey, I've got the right graphics card! I should be all set, right?
A: Unfortunately, there are still a few things to watch out for. Because Windows Vista was just released, a lot of the Vista drivers are still evolving toward stability and performance. You may see some problems with early versions of graphics drivers. Windows Update should automatically keep you up to date with driver updates, but it may be worth checking with your graphics card manufacturer for updated drivers if you are having problems."