I'm running Sims 2 on Windows 7. For the most part it runs better than it did on Vista for me, only:

A) The edges are sharp and I can't soften them, but a quick Google informs me that this is the result of a lousy graphics card, not Vista.

B) When I first ran it on Vista, it wouldn't let me take screenshots. I found out that I could fix this by setting desktop composition to disable while the game is open.

I have a Windows 7 laptop too, and Sims definitely had problems with it. I'd be playing normally and suddenly, for no reason that I could tell, the texture bitmaps for some random object (hair, pinball machine, curtains) would suddenly cover the whole street or ground. Sometimes a texture would cover the ground and another one would cover the street. Sometimes the street and sidewalk would turn black; sometimes my sim's head would turn black. I don't know anything about computers, but since Sims ran fine on Vista I assumed it was Windows 7 and now I play Sims on my sister's computer.

I Googled some but couldn't find anyone else with this problem, so maybe there's something about my computer specifically that doesn't like Sims (or Spore, as a random fun fact)...
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Here may we sit and view their toil
That travail in the deep,
And joy the day in mirth the while,
And spend the night in sleep.

Hmm. Now that you mention it, I have had a few weird texture-swapping issues, but they've been limited to when changing a Sim's appearance or clothing, but I've found that if you just cancel the change and try again, it works normally. Haven't had the terrain issues, though.

I have all the CC I had on my old computer plus some new stuff.