I have the Sapphire ATI 3850 AGP and, while Sims3 will run, its not without significant issues.. and that's after upgrading to the latest drivers from Sapphire (v9.4 hotfix).
Even still, the ATI GPU Recovery will kick-in and I get a black screen until Sims3 decides to finally close out. Also, I have noticed "haze" or "fog" around the trees with the leaves and other Map elements all blocky.. so something is clearly amiss.
To my eyes, it seems to be an issue with certain kinds of transparencies. Example, I also get less severe but still odd graphical artifacts in the trees when playing PerfectWorld - and sometimes clothing, hair, or other objects go "invisible" when passing in front of another transparency.
I run an older machine, but its run games like GuildWars, PerfectWorld, Doom 3, Neverwinter Nights 2, all without problems.
P4 3.4 on Intel D875PBZ board
Sapphire's ATI Radeon HD3850